diff --git a/mlibc/include/stdlib.h b/mlibc/include/stdlib.h
index 43ed3215..cc5f32ea 100644
--- a/mlibc/include/stdlib.h
+++ b/mlibc/include/stdlib.h
@@ -41,6 +41,7 @@ void qsort (void *base, size_t nmemb, size_t size, int (*compar)(void const *, v
 void *realloc (void *p, size_t size);
 long strtol (char const *nptr, char **endptr, int base);
 unsigned long strtoul (char const *nptr, char **endptr, int base);
+unsigned long long strtoull (char const *nptr, char **endptr, int base);
 
 #endif // !(__GNUC__ && POSIX)
 
diff --git a/mlibc/libc-mes+tcc.c b/mlibc/libc-mes+tcc.c
index 0bc5c704..797ff1fb 100644
--- a/mlibc/libc-mes+tcc.c
+++ b/mlibc/libc-mes+tcc.c
@@ -148,6 +148,12 @@ strtoul (char const *nptr, char **endptr, int base)
   return 0;
 }
 
+unsigned long long
+strtoull (char const *nptr, char **endptr, int base)
+{
+  return 0;
+}
+
 time_t time (time_t *tloc)
 {
   return 0;