1 files changed, 15 insertions, 1 deletions

diff --git a/src/lib/libcrypto/bn/bn_word.c b/src/lib/libcrypto/bn/bn_word.c
index c4c6754c37..71654586a1 100644
--- a/src/lib/libcrypto/bn/bn_word.c
+++ b/src/lib/libcrypto/bn/bn_word.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_word.c,v 1.12 2014/07/11 08:44:48 jsing Exp $ */
+/* $OpenBSD: bn_word.c,v 1.13 2016/07/05 02:54:35 bcook Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -73,6 +73,20 @@ BN_mod_word(const BIGNUM *a, BN_ULONG w)
         if (w == 0)
                 return (BN_ULONG) - 1;
 
+#ifndef BN_ULLONG
+        /* If |w| is too long and we don't have |BN_ULLONG| then we need to fall back
+        * to using |BN_div_word|. */
+        if (w > ((BN_ULONG)1 << BN_BITS4)) {
+                BIGNUM *tmp = BN_dup(a);
+                if (tmp == NULL) {
+                        return (BN_ULONG)-1;
+                }
+                ret = BN_div_word(tmp, w);
+                BN_free(tmp);
+                return ret;
+        }
+#endif
+
         bn_check_top(a);
         w &= BN_MASK2;
         for (i = a->top - 1; i >= 0; i--) {