diff --git a/ext/openssl/openssl.c b/ext/openssl/openssl.c
index 4af09b0e0f1cc..aa819be42242f 100644
--- a/ext/openssl/openssl.c
+++ b/ext/openssl/openssl.c
@@ -3524,7 +3524,7 @@ PHP_FUNCTION(openssl_csr_sign)
 		goto cleanup;
 	}
 
-#if PHP_OPENSSL_API_VERSION >= 0x10100
+#if PHP_OPENSSL_API_VERSION >= 0x10100 && !defined (LIBRESSL_VERSION_NUMBER)
 	ASN1_INTEGER_set_int64(X509_get_serialNumber(new_cert), serial);
 #else
 	ASN1_INTEGER_set(X509_get_serialNumber(new_cert), serial);