diff --git a/be/src/exprs/string_functions.cpp b/be/src/exprs/string_functions.cpp
index 32a4261e41..2f3abd2e8e 100644
--- a/be/src/exprs/string_functions.cpp
+++ b/be/src/exprs/string_functions.cpp
@@ -50,10 +50,10 @@ size_t get_char_len(const StringVal& str, std::vector<size_t>* str_index) {
 //  - [optional] len.  No len indicates longest substr possible
 StringVal StringFunctions::substring(FunctionContext* context, const StringVal& str,
                                      const IntVal& pos, const IntVal& len) {
-    if (str.is_null || pos.is_null || len.is_null || pos.val > str.len) {
+    if (str.is_null || pos.is_null || len.is_null) {
         return StringVal::null();
     }
-    if (len.val <= 0 || str.len == 0 || pos.val == 0) {
+    if (len.val <= 0 || str.len == 0 || pos.val == 0 || pos.val > str.len) {
         return StringVal();
     }