diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
index 08491070387bc03ba24ba155d68a70583724c058..b8c96878c9ce0b4f0aa468611a400d2108c861a8 100644
--- a/tools/include/nolibc/sys.h
+++ b/tools/include/nolibc/sys.h
@@ -692,7 +692,7 @@ void *sys_mmap(void *addr, size_t length, int prot, int flags, int fd,
 {
 #ifndef my_syscall6
 	/* Function not implemented. */
-	return -ENOSYS;
+	return (void *)-ENOSYS;
 #else
 
 	int n;