diff --git a/cryptography/hazmat/bindings/openssl/asn1.py b/cryptography/hazmat/bindings/openssl/asn1.py
index dfdf1bf..2edfd2d 100644
--- a/cryptography/hazmat/bindings/openssl/asn1.py
+++ b/cryptography/hazmat/bindings/openssl/asn1.py
@@ -141,6 +141,9 @@
 
 /* These isn't a macro the arg is const on openssl 1.0.2+ */
 int ASN1_GENERALIZEDTIME_check(ASN1_GENERALIZEDTIME *);
+
+/* Not a macro, const on openssl 1.0 */
+int ASN1_STRING_set_default_mask_asc(char *);
 """
 
 CUSTOMIZATIONS = """