diff --git a/src/Microsoft.ML.Data/Data/DataViewUtils.cs b/src/Microsoft.ML.Data/Data/DataViewUtils.cs
index 829118a430..dd06a4610a 100644
--- a/src/Microsoft.ML.Data/Data/DataViewUtils.cs
+++ b/src/Microsoft.ML.Data/Data/DataViewUtils.cs
@@ -1123,9 +1123,11 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                     Ch.CheckParam(IsColumnActive(column), nameof(column), "requested column not active.");
                     Ch.CheckParam(column.Index < _colToActive.Length, nameof(column), "requested column is not active or valid for the Schema.");
 
-                    var getter = _getters[_colToActive[column.Index]] as ValueGetter<TValue>;
+                    var originGetter = _getters[_colToActive[column.Index]];
+                    var getter = originGetter as ValueGetter<TValue>;
                     if (getter == null)
-                        throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                        throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                            $"expected type: '{originGetter.GetType().GetGenericArguments().First()}'.");
                     return getter;
                 }
             }
@@ -1312,9 +1314,11 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 Ch.CheckParam(IsColumnActive(column), nameof(column), "requested column not active");
                 Ch.CheckParam(column.Index < _colToActive.Length, nameof(column), "requested column not active or is invalid for the schema. ");
 
-                var getter = _getters[_colToActive[column.Index]] as ValueGetter<TValue>;
+                var originGetter = _getters[_colToActive[column.Index]];
+                var getter = originGetter as ValueGetter<TValue>;
                 if (getter == null)
-                    throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                        $"expected type: '{originGetter.GetType().GetGenericArguments().First()}'.");
                 return getter;
             }
         }
diff --git a/src/Microsoft.ML.Data/DataLoadSave/Binary/BinaryLoader.cs b/src/Microsoft.ML.Data/DataLoadSave/Binary/BinaryLoader.cs
index 32c9e34cb6..94e6f79720 100644
--- a/src/Microsoft.ML.Data/DataLoadSave/Binary/BinaryLoader.cs
+++ b/src/Microsoft.ML.Data/DataLoadSave/Binary/BinaryLoader.cs
@@ -2035,9 +2035,11 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
             {
                 Ch.CheckParam(column.Index < _colToActivesIndex.Length, nameof(column), "requested column not active.");
 
-                var getter = _pipeGetters[_colToActivesIndex[column.Index]] as ValueGetter<TValue>;
+                var originGetter = _pipeGetters[_colToActivesIndex[column.Index]];
+                var getter = originGetter as ValueGetter<TValue>;
                 if (getter == null)
-                    throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                        $"expected type: '{originGetter.GetType().GetGenericArguments().First()}'.");
                 return getter;
             }
 
diff --git a/src/Microsoft.ML.Data/DataLoadSave/Database/DatabaseLoaderCursor.cs b/src/Microsoft.ML.Data/DataLoadSave/Database/DatabaseLoaderCursor.cs
index f19d96830f..7d029c96a8 100644
--- a/src/Microsoft.ML.Data/DataLoadSave/Database/DatabaseLoaderCursor.cs
+++ b/src/Microsoft.ML.Data/DataLoadSave/Database/DatabaseLoaderCursor.cs
@@ -4,6 +4,7 @@
 
 using System;
 using System.Data.Common;
+using System.Linq;
 using Microsoft.ML.Internal.Utilities;
 using Microsoft.ML.Runtime;
 
@@ -158,9 +159,11 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 Ch.CheckParam(column.Index < _getters.Length, nameof(column), "requested column not valid.");
                 Ch.Check(IsColumnActive(column));
 
-                var fn = _getters[column.Index] as ValueGetter<TValue>;
+                var originFn = _getters[column.Index];
+                var fn = originFn as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                        $"expected type: '{originFn.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
 
diff --git a/src/Microsoft.ML.Data/DataLoadSave/Text/TextLoaderCursor.cs b/src/Microsoft.ML.Data/DataLoadSave/Text/TextLoaderCursor.cs
index 5cdca75e86..d784d280eb 100644
--- a/src/Microsoft.ML.Data/DataLoadSave/Text/TextLoaderCursor.cs
+++ b/src/Microsoft.ML.Data/DataLoadSave/Text/TextLoaderCursor.cs
@@ -5,6 +5,7 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -318,9 +319,11 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 Ch.CheckParam(column.Index < _getters.Length, nameof(column), "requested column not valid.");
                 Ch.Check(IsColumnActive(column));
 
-                var fn = _getters[column.Index] as ValueGetter<TValue>;
+                var originFn = _getters[column.Index];
+                var fn = originFn as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                        $"expected type: '{originFn.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
 
diff --git a/src/Microsoft.ML.Data/DataLoadSave/Transpose/TransposeLoader.cs b/src/Microsoft.ML.Data/DataLoadSave/Transpose/TransposeLoader.cs
index 6339333cef..8a0ee23f1a 100644
--- a/src/Microsoft.ML.Data/DataLoadSave/Transpose/TransposeLoader.cs
+++ b/src/Microsoft.ML.Data/DataLoadSave/Transpose/TransposeLoader.cs
@@ -693,7 +693,8 @@ public override ValueGetter<VBuffer<TValue>> GetGetter<TValue>()
             {
                 ValueGetter<VBuffer<TValue>> getter = _getter as ValueGetter<VBuffer<TValue>>;
                 if (getter == null)
-                    throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                        $"expected type: '{_getter.GetType().GetGenericArguments().First().GetGenericArguments().First()}'.");
                 return getter;
             }
 
@@ -883,9 +884,11 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 Ch.CheckParam(column.Index <= _colToActivesIndex.Length && IsColumnActive(column), nameof(column), "requested column not active");
                 Ch.AssertValue(_getters[_colToActivesIndex[column.Index]]);
 
-                var getter = _getters[_colToActivesIndex[column.Index]] as ValueGetter<TValue>;
+                var originGetter = _getters[_colToActivesIndex[column.Index]];
+                var getter = originGetter as ValueGetter<TValue>;
                 if (getter == null)
-                    throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                        $"expected type: '{originGetter.GetType().GetGenericArguments().First()}'.");
                 return getter;
             }
         }
diff --git a/src/Microsoft.ML.Data/DataView/AppendRowsDataView.cs b/src/Microsoft.ML.Data/DataView/AppendRowsDataView.cs
index 0773507497..793b2eba13 100644
--- a/src/Microsoft.ML.Data/DataView/AppendRowsDataView.cs
+++ b/src/Microsoft.ML.Data/DataView/AppendRowsDataView.cs
@@ -190,9 +190,12 @@ public sealed override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Colu
             {
                 Ch.CheckParam(column.Index <= Getters.Length && IsColumnActive(column), nameof(column), "requested column not active");
 
-                if (!(Getters[column.Index] is ValueGetter<TValue>))
-                    throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}'");
-                return Getters[column.Index] as ValueGetter<TValue>;
+                var originGetter = Getters[column.Index];
+                var getter = originGetter as ValueGetter<TValue>;
+                if (getter == null)
+                    throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                        $"expected type: '{originGetter.GetType().GetGenericArguments().First()}'.");
+                return getter;
             }
 
             /// <summary>
diff --git a/src/Microsoft.ML.Data/DataView/ArrayDataViewBuilder.cs b/src/Microsoft.ML.Data/DataView/ArrayDataViewBuilder.cs
index e4b7b754f2..e5aa1383d8 100644
--- a/src/Microsoft.ML.Data/DataView/ArrayDataViewBuilder.cs
+++ b/src/Microsoft.ML.Data/DataView/ArrayDataViewBuilder.cs
@@ -325,9 +325,11 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                     Ch.Check(column.Index < Schema.Count);
                     Ch.Check(column.Index < _active.Length && _active[column.Index], "the requested column is not active");
 
-                    var columnValue = _view._columns[column.Index] as Column<TValue>;
+                    var originColumnValue = _view._columns[column.Index];
+                    var columnValue = originColumnValue as Column<TValue>;
                     if (columnValue == null)
-                        throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                        throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                            $"expected type: '{originColumnValue.Type.RawType}'.");
 
                     return
                         (ref TValue value) =>
diff --git a/src/Microsoft.ML.Data/DataView/BatchDataViewMapperBase.cs b/src/Microsoft.ML.Data/DataView/BatchDataViewMapperBase.cs
index e1cde83032..623591556a 100644
--- a/src/Microsoft.ML.Data/DataView/BatchDataViewMapperBase.cs
+++ b/src/Microsoft.ML.Data/DataView/BatchDataViewMapperBase.cs
@@ -122,7 +122,8 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 Ch.Assert(getter != null);
                 var fn = getter as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                            $"expected type: '{getter.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
 
diff --git a/src/Microsoft.ML.Data/DataView/CacheDataView.cs b/src/Microsoft.ML.Data/DataView/CacheDataView.cs
index dffa6aa4dd..a0f5ad4d31 100644
--- a/src/Microsoft.ML.Data/DataView/CacheDataView.cs
+++ b/src/Microsoft.ML.Data/DataView/CacheDataView.cs
@@ -1206,9 +1206,11 @@ public sealed override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Colu
                 Ch.CheckParam(column.Index <= _colToActivesIndex.Length && IsColumnActive(column), nameof(column), "requested column not active");
                 Ch.Check(_colToActivesIndex[column.Index] < _getters.Length);
 
-                var getter = _getters[_colToActivesIndex[column.Index]] as ValueGetter<TValue>;
+                var originGetter = _getters[_colToActivesIndex[column.Index]];
+                var getter = originGetter as ValueGetter<TValue>;
                 if (getter == null)
-                    throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                        $"expected type: '{originGetter.GetType().GetGenericArguments().First()}'.");
                 return getter;
             }
 
diff --git a/src/Microsoft.ML.Data/DataView/DataViewConstructionUtils.cs b/src/Microsoft.ML.Data/DataView/DataViewConstructionUtils.cs
index 8d79076c05..9846587f3d 100644
--- a/src/Microsoft.ML.Data/DataView/DataViewConstructionUtils.cs
+++ b/src/Microsoft.ML.Data/DataView/DataViewConstructionUtils.cs
@@ -427,7 +427,8 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 Contracts.AssertValue(getter);
                 var fn = getter as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Host.Except("Invalid TValue in GetGetter for column #{0}: '{1}'", column, typeof(TValue));
+                    throw Host.Except($"Invalid TValue in GetGetter for column #{column}: '{typeof(TValue)}', " +
+                        $"expected type: '{getter.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
         }
diff --git a/src/Microsoft.ML.Data/DataView/RowToRowMapperTransform.cs b/src/Microsoft.ML.Data/DataView/RowToRowMapperTransform.cs
index efb86af7ca..3747e361ff 100644
--- a/src/Microsoft.ML.Data/DataView/RowToRowMapperTransform.cs
+++ b/src/Microsoft.ML.Data/DataView/RowToRowMapperTransform.cs
@@ -333,10 +333,12 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 if (isSrc)
                     return Input.GetGetter<TValue>(Input.Schema[index]);
 
-                Contracts.Assert(_getters[index] != null);
-                var fn = _getters[index] as ValueGetter<TValue>;
+                var originFn = _getters[index];
+                Contracts.Assert(originFn != null);
+                var fn = originFn as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Contracts.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Contracts.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                        $"expected type: '{originFn.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
 
@@ -402,7 +404,8 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 Ch.Assert(getter != null);
                 var fn = getter as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Contracts.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                        $"expected type: '{getter.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
 
diff --git a/src/Microsoft.ML.Data/DataView/Transposer.cs b/src/Microsoft.ML.Data/DataView/Transposer.cs
index 0d317f0887..c30843e37a 100644
--- a/src/Microsoft.ML.Data/DataView/Transposer.cs
+++ b/src/Microsoft.ML.Data/DataView/Transposer.cs
@@ -317,7 +317,8 @@ public override ValueGetter<VBuffer<TValue>> GetGetter<TValue>()
                     _getter = GetGetterCore();
                 ValueGetter<VBuffer<TValue>> getter = _getter as ValueGetter<VBuffer<TValue>>;
                 if (getter == null)
-                    throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                        $"expected type: '{_getter.GetType().GetGenericArguments().First().GetGenericArguments().First()}'.");
                 return getter;
             }
 
@@ -1167,9 +1168,11 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                         {
                             Contracts.Check(IsColumnActive(column) && column.Index < _getters.Length);
                             Contracts.AssertValue(_getters[column.Index]);
-                            var fn = _getters[column.Index] as ValueGetter<TValue>;
+                            var originFn = _getters[column.Index];
+                            var fn = originFn as ValueGetter<TValue>;
                             if (fn == null)
-                                throw Contracts.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                                throw Contracts.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                                    $"expected type: '{originFn.GetType().GetGenericArguments().First()}'.");
                             return fn;
                         }
 
@@ -1501,7 +1504,8 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
 
                     var getter = _getter as ValueGetter<TValue>;
                     if (getter == null)
-                        throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                        throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                            $"expected type: '{_getter.GetType().GetGenericArguments().First()}'.");
                     return getter;
                 }
 
diff --git a/src/Microsoft.ML.Data/Scorers/RowToRowScorerBase.cs b/src/Microsoft.ML.Data/Scorers/RowToRowScorerBase.cs
index 1bc5561942..ad3f87441f 100644
--- a/src/Microsoft.ML.Data/Scorers/RowToRowScorerBase.cs
+++ b/src/Microsoft.ML.Data/Scorers/RowToRowScorerBase.cs
@@ -300,7 +300,8 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 Ch.Assert(getter != null);
                 var fn = getter as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                            $"expected type: '{getter.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
         }
diff --git a/src/Microsoft.ML.Data/Transforms/GenerateNumberTransform.cs b/src/Microsoft.ML.Data/Transforms/GenerateNumberTransform.cs
index bacc0a888b..1dc8ad878e 100644
--- a/src/Microsoft.ML.Data/Transforms/GenerateNumberTransform.cs
+++ b/src/Microsoft.ML.Data/Transforms/GenerateNumberTransform.cs
@@ -439,10 +439,12 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 if (isSrc)
                     return Input.GetGetter<TValue>(Input.Schema[index]);
 
-                Ch.Assert(_getters[index] != null);
-                var fn = _getters[index] as ValueGetter<TValue>;
+                var originFn = _getters[index];
+                Ch.Assert(originFn != null);
+                var fn = originFn as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                            $"expected type: '{originFn.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
 
diff --git a/src/Microsoft.ML.Data/Transforms/LabelConvertTransform.cs b/src/Microsoft.ML.Data/Transforms/LabelConvertTransform.cs
index 7731135d12..e14c07d2ab 100644
--- a/src/Microsoft.ML.Data/Transforms/LabelConvertTransform.cs
+++ b/src/Microsoft.ML.Data/Transforms/LabelConvertTransform.cs
@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Linq;
 using System.Text;
 using System.Threading;
 using Microsoft.ML;
@@ -223,7 +224,8 @@ public override ValueGetter<VBuffer<TValue>> GetGetter<TValue>()
             {
                 ValueGetter<VBuffer<TValue>> getter = _getter as ValueGetter<VBuffer<TValue>>;
                 if (getter == null)
-                    throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                            $"expected type: '{_getter.GetType().GetGenericArguments().First().GetGenericArguments().First()}'.");
                 return getter;
             }
         }
diff --git a/src/Microsoft.ML.Data/Transforms/NAFilter.cs b/src/Microsoft.ML.Data/Transforms/NAFilter.cs
index 620594fb13..5d24f7fa93 100644
--- a/src/Microsoft.ML.Data/Transforms/NAFilter.cs
+++ b/src/Microsoft.ML.Data/Transforms/NAFilter.cs
@@ -426,9 +426,11 @@ private bool TryGetColumnValueGetter<TValue>(int col, out ValueGetter<TValue> fn
                     return false;
                 }
 
-                fn = _values[index].GetGetter() as ValueGetter<TValue>;
+                var originFn = _values[index].GetGetter();
+                fn = originFn as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                            $"expected type: '{originFn.GetType().GetGenericArguments().First()}'.");
                 return true;
             }
 
diff --git a/src/Microsoft.ML.Data/Transforms/PerGroupTransformBase.cs b/src/Microsoft.ML.Data/Transforms/PerGroupTransformBase.cs
index 8c5322bc19..703b574f90 100644
--- a/src/Microsoft.ML.Data/Transforms/PerGroupTransformBase.cs
+++ b/src/Microsoft.ML.Data/Transforms/PerGroupTransformBase.cs
@@ -305,7 +305,8 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 Ch.Assert(getter != null);
                 var fn = getter as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                            $"expected type: '{getter.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
 
diff --git a/src/Microsoft.ML.Data/Transforms/RangeFilter.cs b/src/Microsoft.ML.Data/Transforms/RangeFilter.cs
index a1faa00ef2..db131a782e 100644
--- a/src/Microsoft.ML.Data/Transforms/RangeFilter.cs
+++ b/src/Microsoft.ML.Data/Transforms/RangeFilter.cs
@@ -321,9 +321,11 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
 
                 if (column.Index != Parent._index)
                     return Input.GetGetter<TValue>(column);
-                var fn = GetGetter() as ValueGetter<TValue>;
+                var originFn = GetGetter();
+                var fn = originFn as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                            $"expected type: '{originFn.GetType().GetGenericArguments().First()}'.");
 
                 return fn;
             }
diff --git a/src/Microsoft.ML.Data/Transforms/RowShufflingTransformer.cs b/src/Microsoft.ML.Data/Transforms/RowShufflingTransformer.cs
index 090a34049e..050dfb8753 100644
--- a/src/Microsoft.ML.Data/Transforms/RowShufflingTransformer.cs
+++ b/src/Microsoft.ML.Data/Transforms/RowShufflingTransformer.cs
@@ -4,6 +4,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using System.Threading.Tasks.Dataflow;
@@ -731,9 +732,12 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
             {
                 Ch.CheckParam(column.Index < _colToActivesIndex.Length, nameof(column));
                 Ch.CheckParam(_colToActivesIndex[column.Index] >= 0, nameof(column), "requested column not active");
-                ValueGetter<TValue> getter = _getters[_colToActivesIndex[column.Index]] as ValueGetter<TValue>;
+
+                var originGetter = _getters[_colToActivesIndex[column.Index]];
+                ValueGetter<TValue> getter = originGetter as ValueGetter<TValue>;
                 if (getter == null)
-                    throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                            $"expected type: '{originGetter.GetType().GetGenericArguments().First()}'.");
                 return getter;
             }
         }
diff --git a/src/Microsoft.ML.Data/Transforms/TransformBase.cs b/src/Microsoft.ML.Data/Transforms/TransformBase.cs
index 3fe8d0bc37..8d21772607 100644
--- a/src/Microsoft.ML.Data/Transforms/TransformBase.cs
+++ b/src/Microsoft.ML.Data/Transforms/TransformBase.cs
@@ -229,10 +229,12 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 if (isSrc)
                     return Input.GetGetter<TValue>(Input.Schema[index]);
 
-                Contracts.Assert(_getters[index] != null);
-                var fn = _getters[index] as ValueGetter<TValue>;
+                var originFn = _getters[index];
+                Contracts.Assert(originFn != null);
+                var fn = originFn as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Contracts.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Contracts.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                            $"expected type: '{originFn.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
 
@@ -901,10 +903,12 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 if (isSrc)
                     return Input.GetGetter<TValue>(Input.Schema[index]);
 
-                Ch.Assert(_getters[index] != null);
-                var fn = _getters[index] as ValueGetter<TValue>;
+                var originFn = _getters[index];
+                Ch.Assert(originFn != null);
+                var fn = originFn as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                            $"expected type: '{originFn.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
 
diff --git a/src/Microsoft.ML.Featurizers/TimeSeriesImputerDataView.cs b/src/Microsoft.ML.Featurizers/TimeSeriesImputerDataView.cs
index c5fc0f038b..f5bc2d7db0 100644
--- a/src/Microsoft.ML.Featurizers/TimeSeriesImputerDataView.cs
+++ b/src/Microsoft.ML.Featurizers/TimeSeriesImputerDataView.cs
@@ -792,9 +792,11 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
             {
                 _ch.Check(IsColumnActive(column));
 
-                var fn = _allColumns[column.Name].GetGetter() as ValueGetter<TValue>;
+                var originFn = _allColumns[column.Name].GetGetter();
+                var fn = originFn as ValueGetter<TValue>;
                 if (fn == null)
-                    throw _ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw _ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                            $"expected type: '{originFn.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
 
diff --git a/src/Microsoft.ML.Parquet/ParquetLoader.cs b/src/Microsoft.ML.Parquet/ParquetLoader.cs
index 443367089f..54a109396a 100644
--- a/src/Microsoft.ML.Parquet/ParquetLoader.cs
+++ b/src/Microsoft.ML.Parquet/ParquetLoader.cs
@@ -599,9 +599,11 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
             {
                 Ch.CheckParam(IsColumnActive(column), nameof(column), "requested column not active");
 
-                var getter = _getters[_colToActivesIndex[column.Index]] as ValueGetter<TValue>;
+                var originGetter = _getters[_colToActivesIndex[column.Index]];
+                var getter = originGetter as ValueGetter<TValue>;
                 if (getter == null)
-                    throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                            $"expected type: '{originGetter.GetType().GetGenericArguments().First()}'.");
 
                 return getter;
             }
diff --git a/src/Microsoft.ML.Parquet/PartitionedFileLoader.cs b/src/Microsoft.ML.Parquet/PartitionedFileLoader.cs
index 863662eeed..77cf72f92e 100644
--- a/src/Microsoft.ML.Parquet/PartitionedFileLoader.cs
+++ b/src/Microsoft.ML.Parquet/PartitionedFileLoader.cs
@@ -421,11 +421,11 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
             {
                 Ch.Check(IsColumnActive(column));
 
-                var getter = _getters[column.Index] as ValueGetter<TValue>;
+                var originGetter = _getters[column.Index];
+                var getter = originGetter as ValueGetter<TValue>;
                 if (getter == null)
-                {
-                    throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
-                }
+                    throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                            $"expected type: '{originGetter.GetType().GetGenericArguments().First()}'.");
 
                 return getter;
             }
diff --git a/src/Microsoft.ML.TimeSeries/SequentialTransformerBase.cs b/src/Microsoft.ML.TimeSeries/SequentialTransformerBase.cs
index 4ffe27b31f..bbfa20e7c2 100644
--- a/src/Microsoft.ML.TimeSeries/SequentialTransformerBase.cs
+++ b/src/Microsoft.ML.TimeSeries/SequentialTransformerBase.cs
@@ -987,10 +987,12 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 if (isSrc)
                     return _input.GetGetter<TValue>(column);
 
-                Contracts.Assert(_getters[index] != null);
-                var fn = _getters[index] as ValueGetter<TValue>;
+                var originFn = _getters[index];
+                Contracts.Assert(originFn != null);
+                var fn = originFn as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Contracts.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Contracts.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                            $"expected type: '{originFn.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
 
@@ -1061,7 +1063,8 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 Ch.AssertValue(getter);
                 if (getter is ValueGetter<TValue> fn)
                     return fn;
-                throw Ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                            $"expected type: '{getter.GetType().GetGenericArguments().First()}'.");
             }
 
             protected override void Dispose(bool disposing)
diff --git a/src/Microsoft.ML.Transforms/OptionalColumnTransform.cs b/src/Microsoft.ML.Transforms/OptionalColumnTransform.cs
index 98b100c15f..dc4ddb3a82 100644
--- a/src/Microsoft.ML.Transforms/OptionalColumnTransform.cs
+++ b/src/Microsoft.ML.Transforms/OptionalColumnTransform.cs
@@ -485,10 +485,12 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 if (_getters[index] == null)
                     return Input.GetGetter<TValue>(_bindings.AsSchema[_bindings.SrcCols[index]]);
 
-                Ch.Assert(_getters[index] != null);
-                var fn = _getters[index] as ValueGetter<TValue>;
+                var originFn = _getters[index];
+                Ch.Assert(originFn != null);
+                var fn = originFn as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                            $"expected type: '{originFn.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
 
diff --git a/src/Microsoft.ML.Transforms/ProduceIdTransform.cs b/src/Microsoft.ML.Transforms/ProduceIdTransform.cs
index f9062319ce..f495215e37 100644
--- a/src/Microsoft.ML.Transforms/ProduceIdTransform.cs
+++ b/src/Microsoft.ML.Transforms/ProduceIdTransform.cs
@@ -219,7 +219,8 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 Ch.AssertValue(idGetter);
                 var fn = idGetter as ValueGetter<TValue>;
                 if (fn == null)
-                    throw Ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                    throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                            $"expected type: '{idGetter.GetType().GetGenericArguments().First()}'.");
                 return fn;
             }
         }
diff --git a/src/Microsoft.ML.Transforms/StatefulCustomMappingTransformer.cs b/src/Microsoft.ML.Transforms/StatefulCustomMappingTransformer.cs
index 9b94c859bb..cb0e0b20ed 100644
--- a/src/Microsoft.ML.Transforms/StatefulCustomMappingTransformer.cs
+++ b/src/Microsoft.ML.Transforms/StatefulCustomMappingTransformer.cs
@@ -318,10 +318,12 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                     if (isSrc)
                         return Input.GetGetter<TValue>(Input.Schema[index]);
 
-                    Ch.Assert(_getters[index] != null);
-                    var fn = _getters[index] as ValueGetter<TValue>;
+                    var originFn = _getters[index];
+                    Ch.Assert(originFn != null);
+                    var fn = originFn as ValueGetter<TValue>;
                     if (fn == null)
-                        throw Ch.Except("Invalid TValue in GetGetter: '{0}'", typeof(TValue));
+                        throw Ch.Except($"Invalid TValue in GetGetter: '{typeof(TValue)}', " +
+                            $"expected type: '{originFn.GetType().GetGenericArguments().First()}'.");
                     return fn;
                 }
 
diff --git a/src/Microsoft.ML.Transforms/SvmLight/SvmLightLoader.cs b/src/Microsoft.ML.Transforms/SvmLight/SvmLightLoader.cs
index aaa116498b..346d0acd8d 100644
--- a/src/Microsoft.ML.Transforms/SvmLight/SvmLightLoader.cs
+++ b/src/Microsoft.ML.Transforms/SvmLight/SvmLightLoader.cs
@@ -480,9 +480,11 @@ public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column colu
                 {
                     Ch.CheckParam(column.Index == 0, nameof(column));
                     Ch.CheckParam(_isActive, nameof(column), "requested column not active");
+
                     ValueGetter<TValue> getter = _getter as ValueGetter<TValue>;
                     if (getter == null)
-                        throw Ch.Except("Invalid TValue: '{0}'", typeof(TValue));
+                        throw Ch.Except($"Invalid TValue: '{typeof(TValue)}', " +
+                            $"expected type: '{_getter.GetType().GetGenericArguments().First()}'.");
                     return getter;
                 }