diff --git a/modules/core/src/gpumat.cpp b/modules/core/src/gpumat.cpp
index bf128fbcd..0baa8645f 100644
--- a/modules/core/src/gpumat.cpp
+++ b/modules/core/src/gpumat.cpp
@@ -761,7 +761,7 @@ namespace
 
 namespace cv { namespace gpu { namespace device
 {
-    void copyToWithMask_gpu(DevMem2Db src, DevMem2Db dst, size_t elemSize1, int cn, DevMem2Db mask, bool colorMask, cudaStream_t stream);
+    void copyToWithMask_gpu(DevMem2Db src, DevMem2Db dst, int elemSize1, int cn, DevMem2Db mask, bool colorMask, cudaStream_t stream);
 
     template <typename T>
     void set_to_gpu(DevMem2Db mat, const T* scalar, int channels, cudaStream_t stream);