diff --git a/include/picotls.h b/include/picotls.h
index 70abcf8..bbf3739 100644
--- a/include/picotls.h
+++ b/include/picotls.h
@@ -986,7 +986,11 @@
      */
     struct {
         uint8_t bytes[PTLS_SHA256_DIGEST_SIZE];
+#ifdef _WINDOWS
+        unsigned int is_set : 1;
+#else
         uint8_t is_set : 1;
+#endif
     } ticket_context;
     /**
      * (optional) list of CAs advertised to clients as supported in the CertificateRequest message; each item must be DNs in DER