diff --git a/src/cryptography/hazmat/bindings/openssl/x509v3.py b/src/cryptography/hazmat/bindings/openssl/x509v3.py
index 13bf9a2..28dd7f3 100644
--- a/src/cryptography/hazmat/bindings/openssl/x509v3.py
+++ b/src/cryptography/hazmat/bindings/openssl/x509v3.py
@@ -106,6 +106,9 @@
 """
 
 MACROS = """
+/* This is a macro defined by a call to DECLARE_ASN1_FUNCTIONS in the
+   x509v3.h header. */
+void BASIC_CONSTRAINTS_free(BASIC_CONSTRAINTS *);
 void *X509V3_set_ctx_nodb(X509V3_CTX *);
 int sk_GENERAL_NAME_num(struct stack_st_GENERAL_NAME *);
 int sk_GENERAL_NAME_push(struct stack_st_GENERAL_NAME *, GENERAL_NAME *);