1 files changed, 4 insertions, 1 deletions

diff --git a/src/lib/libcrypto/bn/bn_mont.c b/src/lib/libcrypto/bn/bn_mont.c
index 45e312a3a6..e01af702e7 100644
--- a/src/lib/libcrypto/bn/bn_mont.c
+++ b/src/lib/libcrypto/bn/bn_mont.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_mont.c,v 1.27 2021/12/04 16:05:46 tb Exp $ */
+/* $OpenBSD: bn_mont.c,v 1.28 2022/02/07 19:44:23 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -369,6 +369,9 @@ BN_MONT_CTX_set(BN_MONT_CTX *mont, const BIGNUM *mod, BN_CTX *ctx)
         int ret = 0;
         BIGNUM *Ri, *R;
 
+        if (BN_is_zero(mod))
+                return 0;
+
         BN_CTX_start(ctx);
         if ((Ri = BN_CTX_get(ctx)) == NULL)
                 goto err;