BN_cmp macro
diff --git a/cryptography/hazmat/bindings/openssl/bignum.py b/cryptography/hazmat/bindings/openssl/bignum.py
index 48350a3..d505b17 100644
--- a/cryptography/hazmat/bindings/openssl/bignum.py
+++ b/cryptography/hazmat/bindings/openssl/bignum.py
@@ -92,6 +92,7 @@
 int BN_zero(BIGNUM *);
 int BN_one(BIGNUM *);
 int BN_mod(BIGNUM *, const BIGNUM *, const BIGNUM *, BN_CTX *);
+BIGNUM *BN_cmp(const BIGNUM *, const BIGNUM *);
 """
 
 CUSTOMIZATIONS = """