diff --git a/src/metric.jl b/src/metric.jl
index 7916d45b639c..7e76b969d0a0 100644
--- a/src/metric.jl
+++ b/src/metric.jl
@@ -36,6 +36,19 @@ set.
 =#
 abstract AbstractEvalMetric
 
+# Generic update! version
+function update!{T <: AbstractEvalMetric}(metric :: T, labels :: Vector{NDArray}, preds :: Vector{NDArray})
+  if length(labels) != length(preds)
+    Base.warn_once(
+      "The number of labels ($(length(labels))) does not correspond to the\
+      number of outputs ($(length(preds))). The calculated metric might not be accuracte.")
+  end
+  for (label, pred) in zip(labels, preds)
+    _update_single_output(metric, label, pred)
+  end
+end
+
+
 #=doc
 .. class:: Accuracy
 
@@ -85,13 +98,6 @@ function _update_single_output(metric :: Accuracy, label :: NDArray, pred :: NDA
   end
 end
 
-function update!(metric :: Accuracy, labels :: Vector{NDArray}, preds :: Vector{NDArray})
-  @assert length(labels) == length(preds)
-  for i = 1:length(labels)
-    _update_single_output(metric, labels[i], preds[i])
-  end
-end
-
 import Base: get
 function get(metric :: Accuracy)
   return [(:accuracy, metric.acc_sum / metric.n_sample)]
@@ -129,13 +135,6 @@ function _update_single_output(metric :: MSE, label :: NDArray, pred :: NDArray)
   end
 end
 
-function update!(metric :: MSE, labels :: Vector{NDArray}, preds :: Vector{NDArray})
-  @assert length(labels) == length(preds)
-  for i = 1:length(labels)
-    _update_single_output(metric, labels[i], preds[i])
-  end
-end
-
 function get(metric :: MSE)
   return [(:MSE, metric.mse_sum / metric.n_sample)]
 end
@@ -193,13 +192,6 @@ function _update_single_output(metric :: ACE, label :: NDArray, pred :: NDArray)
   end
 end
 
-function update!(metric :: ACE, labels :: Vector{NDArray}, preds :: Vector{NDArray})
-  @assert length(labels) == length(preds)
-  for i = 1:length(labels)
-    _update_single_output(metric, labels[i], preds[i])
-  end
-end
-
 #=doc
 .. class:: MultiACE
 
@@ -251,9 +243,3 @@ function _update_single_output(metric :: MultiACE, label :: NDArray, pred :: NDA
   end
 end
 
-function update!(metric :: MultiACE, labels :: Vector{NDArray}, preds :: Vector{NDArray})
-  @assert length(labels) == length(preds)
-  for i = 1:length(labels)
-    _update_single_output(metric, labels[i], preds[i])
-  end
-end