diff --git a/src/mbyte.c b/src/mbyte.c
index 61a7d8b..ce0c897 100644
--- a/src/mbyte.c
+++ b/src/mbyte.c
@@ -4129,7 +4129,7 @@
 	done = to - (char *)result;
     }
 
-    if (resultlenp != NULL)
+    if (resultlenp != NULL && result != NULL)
 	*resultlenp = (int)(to - (char *)result);
     return result;
 }