diff --git a/src/transports/winhttp.c b/src/transports/winhttp.c
index 0be73aeda..1034a1cbd 100644
--- a/src/transports/winhttp.c
+++ b/src/transports/winhttp.c
@@ -53,6 +53,10 @@
 # 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