diff --git a/lib/md5.h b/lib/md5.h
index 89b9a32..3ce83a6 100644
--- a/lib/md5.h
+++ b/lib/md5.h
@@ -82,4 +82,7 @@
 	md5_result((x), (y));	\
 } while (0)
 
+/* From RFC 2104 */
+void hmac_md5(unsigned char* text, int text_len, unsigned char* key, int key_len, caddr_t digest);
+
 #endif /* ! _LIBZEBRA_MD5_H_*/