--- a/compiler/libs.md4.c
+++ b/compiler/libs.md4.c
@@ -52,7 +52,7 @@
 static void mdfour_begin(struct mdfour *md);
 static void mdfour_update(struct mdfour *md, const unsigned char *in, int n);
 static void mdfour_tail(struct mdfour *m, const unsigned char *in, int n);
-static void mdfour_result(const struct mdfour *md, unsigned char out[12]);
+static void mdfour_result(const struct mdfour *md, unsigned char *out);