diff --git a/crypto/bn/bn_asm.c b/crypto/bn/bn_asm.c
index a5dc574fd..be8aa3ffc 100644
--- a/crypto/bn/bn_asm.c
+++ b/crypto/bn/bn_asm.c
@@ -296,7 +296,7 @@ BN_ULONG bn_div_words(BN_ULONG h, BN_ULONG l, BN_ULONG d)
 #endif /* !defined(BN_LLONG) && defined(BN_DIV2W) */
 
 #ifdef BN_LLONG
-BN_ULONG bn_add_words(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b, int n)
+BN_ULONG bn_add_words(BN_ULONG *r, const BN_ULONG *a, const BN_ULONG *b, int n)
         {
 	BN_ULLONG ll=0;