diff --git a/browser/GMPolyfill.js b/browser/GMPolyfill.js
index 6f05ca0b..beee9156 100644
--- a/browser/GMPolyfill.js
+++ b/browser/GMPolyfill.js
@@ -59,8 +59,8 @@ async function checkCors(url, method) {
     const origin = headers["access-control-allow-origin"];
     if (origin !== "*" && origin !== window.location.origin) return false;
 
-    const methods = headers["access-control-allow-methods"]?.split(/,\s/g);
-    if (methods && !methods.includes(method)) return false;
+    const methods = headers["access-control-allow-methods"]?.toLowerCase().split(/,\s/g);
+    if (methods && !methods.includes(method.toLowerCase())) return false;
 
     return true;
 }