diff --git a/src/patcher.ts b/src/patcher.ts
index 8e28fd10..a1aba2d8 100644
--- a/src/patcher.ts
+++ b/src/patcher.ts
@@ -57,6 +57,11 @@ electron.app.whenReady().then(() => {
         if (responseHeaders) {
             delete responseHeaders["content-security-policy-report-only"];
             delete responseHeaders["content-security-policy"];
+
+            // Fix hosts that don't properly set the content type, such as
+            // raw.githubusercontent.com
+            if (url.endsWith(".css"))
+                responseHeaders["content-type"] = ["text/css"];
         }
         cb({ cancel: false, responseHeaders });
     });