diff --git a/modules/core/src/copy.cpp b/modules/core/src/copy.cpp
index 894776bb32..b87d080de5 100644
--- a/modules/core/src/copy.cpp
+++ b/modules/core/src/copy.cpp
@@ -286,6 +286,7 @@ void Mat::copyTo( OutputArray _dst, InputArray _mask ) const
 
     if( dims <= 2 )
     {
+        CV_Assert( size() == mask.size() );
         Size sz = getContinuousSize(*this, dst, mask, mcn);
         copymask(data, step, mask.data, mask.step, dst.data, dst.step, sz, &esz);
         return;