diff --git a/libc/private/bionic_mbstate.h b/libc/private/bionic_mbstate.h
index 292959a..352115a 100644
--- a/libc/private/bionic_mbstate.h
+++ b/libc/private/bionic_mbstate.h
@@ -29,6 +29,7 @@
 #ifndef _BIONIC_MBSTATE_H
 #define _BIONIC_MBSTATE_H
 
+#include <errno.h>
 #include <wchar.h>
 
 __BEGIN_DECLS