diff --git a/client/mysqltest.c b/client/mysqltest.c
index 628a4e639fd..ad9e7452430 100644
--- a/client/mysqltest.c
+++ b/client/mysqltest.c
@@ -1330,7 +1330,7 @@ void show_diff(DYNAMIC_STRING* ds,
   }
   else
   {
-
+    dynstr_set(&ds_tmp, "");
     /* First try with unified diff */
 
     if (run_tool("diff",