diff --git a/src/multibyte/mbsinit.c b/src/multibyte/mbsinit.c
index d307e5a7..c0e7e494 100644
--- a/src/multibyte/mbsinit.c
+++ b/src/multibyte/mbsinit.c
@@ -13,5 +13,5 @@
 
 int mbsinit(const mbstate_t *st)
 {
-	return !*(unsigned *)st;
+	return !st || !*(unsigned *)st;
 }