diff --git a/src/backend/utils/mb/mbutils.c b/src/backend/utils/mb/mbutils.c
index 345a9d456d4..36bcd9e25a5 100644
--- a/src/backend/utils/mb/mbutils.c
+++ b/src/backend/utils/mb/mbutils.c
@@ -1085,15 +1085,16 @@ pg_mblen_range(const char *mbstr, const char *end)
 	int			length = pg_wchar_table[DatabaseEncoding->encoding].mblen((const unsigned char *) mbstr);
 
 	Assert(end > mbstr);
+
+	if (unlikely(mbstr + length > end))
+		report_invalid_encoding_db(mbstr, length, end - mbstr);
+
 #ifdef VALGRIND_EXPENSIVE
 	VALGRIND_CHECK_MEM_IS_DEFINED(mbstr, end - mbstr);
 #else
 	VALGRIND_CHECK_MEM_IS_DEFINED(mbstr, length);
 #endif
 
-	if (unlikely(mbstr + length > end))
-		report_invalid_encoding_db(mbstr, length, end - mbstr);
-
 	return length;
 }
 
@@ -1108,15 +1109,16 @@ pg_mblen_with_len(const char *mbstr, int limit)
 	int			length = pg_wchar_table[DatabaseEncoding->encoding].mblen((const unsigned char *) mbstr);
 
 	Assert(limit >= 1);
+
+	if (unlikely(length > limit))
+		report_invalid_encoding_db(mbstr, length, limit);
+
 #ifdef VALGRIND_EXPENSIVE
 	VALGRIND_CHECK_MEM_IS_DEFINED(mbstr, limit);
 #else
 	VALGRIND_CHECK_MEM_IS_DEFINED(mbstr, length);
 #endif
 
-	if (unlikely(length > limit))
-		report_invalid_encoding_db(mbstr, length, limit);
-
 	return length;
 }