diff --git a/cupy/cuda/cupy_cudnn.h b/cupy/cuda/cupy_cudnn.h
index 9863ec195f4..2a8cbb6d90f 100644
--- a/cupy/cuda/cupy_cudnn.h
+++ b/cupy/cuda/cupy_cudnn.h
@@ -154,8 +154,6 @@ cudnnStatus_t cudnnSoftmaxBackward(...) {
     return CUDNN_STATUS_SUCCESS;
 }
 
-// ***_v3 functions are not declared in cuDNN v2.
-// Following definitions are for compatibility with cuDNN v3.
 
 typedef enum {} cudnnConvolutionBwdDataAlgo_t;
 typedef enum {} cudnnConvolutionBwdDataPreference_t;
@@ -225,9 +223,6 @@ cudnnStatus_t cudnnSetConvolutionNdDescriptor_v3(...) {
 }
 
 
-// ***_v2 functions are not declared in cuDNN v2 and v3.
-// Following definitions are for compatibility with cuDNN v4.
-
 typedef enum {} cudnnBatchNormMode_t;
 typedef enum {} cudnnNanPropagation_t;