diff --git a/src/Microsoft.ML.Data/Transforms/KeyToVector.cs b/src/Microsoft.ML.Data/Transforms/KeyToVector.cs
index 6c3154104e..d172fbada9 100644
--- a/src/Microsoft.ML.Data/Transforms/KeyToVector.cs
+++ b/src/Microsoft.ML.Data/Transforms/KeyToVector.cs
@@ -705,7 +705,7 @@ private void SaveAsOnnxCore(OnnxContext ctx, int iinfo, ColInfo info, string src
 
                 opType = "OneHotEncoder";
                 var node = ctx.CreateNode(opType, castOutput, encodedVariableName, ctx.GetNodeName(opType));
-                node.AddAttribute("cats_int64s", Enumerable.Range(0, info.TypeSrc.GetItemType().GetKeyCountAsInt32(Host)).Select(x => (long)x));
+                node.AddAttribute("cats_int64s", Enumerable.Range(1, info.TypeSrc.GetItemType().GetKeyCountAsInt32(Host)).Select(x => (long)x));
                 node.AddAttribute("zeros", true);
                 if (_parent._columns[iinfo].OutputCountVector)
                 {
diff --git a/test/BaselineOutput/Common/Onnx/BinaryClassification/BreastCancer/ExcludeVariablesInOnnxConversion.txt b/test/BaselineOutput/Common/Onnx/BinaryClassification/BreastCancer/ExcludeVariablesInOnnxConversion.txt
index b9c6508af7..d37a3a39db 100644
--- a/test/BaselineOutput/Common/Onnx/BinaryClassification/BreastCancer/ExcludeVariablesInOnnxConversion.txt
+++ b/test/BaselineOutput/Common/Onnx/BinaryClassification/BreastCancer/ExcludeVariablesInOnnxConversion.txt
@@ -102,7 +102,6 @@
           {
             "name": "cats_int64s",
             "ints": [
-              "0",
               "1",
               "2",
               "3",
@@ -111,7 +110,8 @@
               "6",
               "7",
               "8",
-              "9"
+              "9",
+              "10"
             ],
             "type": "INTS"
           },
diff --git a/test/BaselineOutput/Common/Onnx/BinaryClassification/BreastCancer/ModelWithLessIO.txt b/test/BaselineOutput/Common/Onnx/BinaryClassification/BreastCancer/ModelWithLessIO.txt
index 9cb2ba4450..22273e89f4 100644
--- a/test/BaselineOutput/Common/Onnx/BinaryClassification/BreastCancer/ModelWithLessIO.txt
+++ b/test/BaselineOutput/Common/Onnx/BinaryClassification/BreastCancer/ModelWithLessIO.txt
@@ -100,7 +100,6 @@
           {
             "name": "cats_int64s",
             "ints": [
-              "0",
               "1",
               "2",
               "3",
@@ -108,7 +107,8 @@
               "5",
               "6",
               "7",
-              "8"
+              "8",
+              "9"
             ],
             "type": "INTS"
           },
diff --git a/test/BaselineOutput/Common/Onnx/BinaryClassification/BreastCancer/OneHotBagPipeline.txt b/test/BaselineOutput/Common/Onnx/BinaryClassification/BreastCancer/OneHotBagPipeline.txt
index 586220cd6c..6822e97818 100644
--- a/test/BaselineOutput/Common/Onnx/BinaryClassification/BreastCancer/OneHotBagPipeline.txt
+++ b/test/BaselineOutput/Common/Onnx/BinaryClassification/BreastCancer/OneHotBagPipeline.txt
@@ -102,7 +102,6 @@
           {
             "name": "cats_int64s",
             "ints": [
-              "0",
               "1",
               "2",
               "3",
@@ -111,7 +110,8 @@
               "6",
               "7",
               "8",
-              "9"
+              "9",
+              "10"
             ],
             "type": "INTS"
           },