diff --git a/sql/field.h b/sql/field.h
index be4d279ce61..dfc02149f9d 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -1151,8 +1151,9 @@ public:
   virtual void reset_fields() {}
   const uchar *ptr_in_record(const uchar *record) const
   {
-    my_ptrdiff_t l_offset= (my_ptrdiff_t) (record -  table->record[0]);
-    return ptr + l_offset;
+    my_ptrdiff_t l_offset= (my_ptrdiff_t) (ptr -  table->record[0]);
+    DBUG_ASSERT(l_offset >= 0 && table->s->rec_buff_length - l_offset > 0);
+    return record + l_offset;
   }
   virtual int set_default();