diff --git a/lib/krb5/crypto-arcfour.c b/lib/krb5/crypto-arcfour.c
index 80d7a7cc7..e195bd3a0 100644
--- a/lib/krb5/crypto-arcfour.c
+++ b/lib/krb5/crypto-arcfour.c
@@ -341,7 +341,7 @@ struct _krb5_encryption_type _krb5_enctype_arcfour_hmac_md5 = {
     &keytype_arcfour,
     &_krb5_checksum_hmac_md5,
     &_krb5_checksum_hmac_md5,
-    F_SPECIAL,
+    F_SPECIAL | F_WEAK,
     ARCFOUR_encrypt,
     0,
     ARCFOUR_prf