diff --git a/crypto/hmac/hmac.c b/crypto/hmac/hmac.c
index d37a249..be2dcce 100644
--- a/crypto/hmac/hmac.c
+++ b/crypto/hmac/hmac.c
@@ -129,7 +129,7 @@
         return 0;
       }
     } else {
-      assert(key_len >= 0 && key_len <= sizeof(key_block));
+      assert(key_len <= sizeof(key_block));
       memcpy(key_block, key, key_len);
       key_block_len = (unsigned)key_len;
     }