define WINHTTP_NO_CLIENT_CERT_CONTEXT if needed
diff --git a/src/transports/winhttp.c b/src/transports/winhttp.c
index 97ceab2..d21c506 100644
--- a/src/transports/winhttp.c
+++ b/src/transports/winhttp.c
@@ -52,6 +52,10 @@
# define WINHTTP_FLAG_SECURE_PROTOCOL_TLS1_3 0x00002000
#endif
+#ifndef WINHTTP_NO_CLIENT_CERT_CONTEXT
+# define WINHTTP_NO_CLIENT_CERT_CONTEXT NULL
+#endif
+
#ifndef HTTP_STATUS_PERMANENT_REDIRECT
# define HTTP_STATUS_PERMANENT_REDIRECT 308
#endif