diff --git a/deps/oblib/src/common/object/ob_obj_funcs.h b/deps/oblib/src/common/object/ob_obj_funcs.h
index 3a11d0ff53..fcf6a6def6 100644
--- a/deps/oblib/src/common/object/ob_obj_funcs.h
+++ b/deps/oblib/src/common/object/ob_obj_funcs.h
@@ -399,7 +399,6 @@ template <>
           ret = OB_SIZE_OVERFLOW;\
         } else {\
           buffer[pos++] = (IS_DOUBLE ? 'D' : 'F');\
-          buffer[pos] = '\0';\
         }\
       }\
     }\
diff --git a/src/sql/engine/dml/ob_link_op.cpp b/src/sql/engine/dml/ob_link_op.cpp
index 6875ebe64a..f7fac1988e 100644
--- a/src/sql/engine/dml/ob_link_op.cpp
+++ b/src/sql/engine/dml/ob_link_op.cpp
@@ -269,7 +269,11 @@ int ObLinkOp::combine_link_stmt(const ObString &link_stmt_fmt,
                K(stmt_fmt_pos), K(stmt_fmt_next_param_pos));
     }
   }
-  if (OB_SUCC(ret)) {
+  if (OB_FAIL(ret)) {
+    // do nothing
+  } else if (link_stmt_pos >= stmt_buf_len_ && OB_FAIL(extend_stmt_buf(link_stmt_pos + 1))) {
+      LOG_WARN("failed to extend stmt buf", K(ret), K(link_stmt_pos), K(stmt_buf_len_));
+  } else {
     stmt_buf_[link_stmt_pos++] = 0;
     LOG_DEBUG("succ to combine link sql", K(stmt_buf_), K(link_stmt_pos));
     if (DBLINK_DRV_OB == link_type_) {