diff --git a/sql/opt_histogram_json.h b/sql/opt_histogram_json.h
index 4cb61e95293..a83e88a88c4 100644
--- a/sql/opt_histogram_json.h
+++ b/sql/opt_histogram_json.h
@@ -61,7 +61,7 @@ public:
   */
   uint get_size() override
   {
-    return size;
+    return (uint)size;
   }
 
   void init_for_collection(MEM_ROOT *mem_root, Histogram_type htype_arg,