diff --git a/src/system/libroot/posix/wchar/mbrtowc.cpp b/src/system/libroot/posix/wchar/mbrtowc.cpp
index 625b11ab13..2dbc35aa2f 100644
--- a/src/system/libroot/posix/wchar/mbrtowc.cpp
+++ b/src/system/libroot/posix/wchar/mbrtowc.cpp
@@ -34,6 +34,8 @@ __mbrtowc(wchar_t* pwc, const char* s, size_t n, mbstate_t* ps)
 
 	if (s == NULL)
 		return __mbrtowc(NULL, "", 1, ps);
+	if (n == 0)
+		return (size_t)-2;
 
 	LocaleBackend* backend = GetCurrentLocaleBackend();