diff --git a/crypto/bn/prime.c b/crypto/bn/prime.c
index bbb8fe0..d07e609 100644
--- a/crypto/bn/prime.c
+++ b/crypto/bn/prime.c
@@ -710,7 +710,7 @@
   if (!BN_add_word(rnd, delta)) {
     return 0;
   }
-  if (BN_num_bits(rnd) != bits) {
+  if (BN_num_bits(rnd) != (unsigned)bits) {
     goto again;
   }