diff --git a/src/common/ob_obj_cast.cpp b/src/common/ob_obj_cast.cpp
index 31d2f591ca3622802e382b5a209d611b4f4676a7..253e93916c50ac141177a8971d82ca1f53351c21 100644
--- a/src/common/ob_obj_cast.cpp
+++ b/src/common/ob_obj_cast.cpp
@@ -107,7 +107,7 @@ static int copy_string(const ObObjCastParams &params,
       } else {
         int64_t zf = params.zf_info_->max_length_ - len;
         if (zf > 0) {
-          MEMSET(buf, 0, zf);
+          MEMSET(buf, '0', zf);
           MEMCPY(buf + zf, str, len);
           len = str_len; // set string length
         } else {