diff --git a/changes/14056-file-ext b/changes/14056-file-ext
new file mode 100644
index 0000000000..ff78c65bcc
--- /dev/null
+++ b/changes/14056-file-ext
@@ -0,0 +1 @@
+* Fixed a bug preventing Windows and Linux users to upload .mobileconfig files in the UI.
diff --git a/frontend/pages/ManageControlsPage/OSSettings/cards/CustomSettings/CustomSettings.tsx b/frontend/pages/ManageControlsPage/OSSettings/cards/CustomSettings/CustomSettings.tsx
index bf27f50674..eb69a5ad1e 100644
--- a/frontend/pages/ManageControlsPage/OSSettings/cards/CustomSettings/CustomSettings.tsx
+++ b/frontend/pages/ManageControlsPage/OSSettings/cards/CustomSettings/CustomSettings.tsx
@@ -61,7 +61,9 @@ const CustomSettings = ({
     const file = files[0];
 
     if (
-      file.type !== "application/x-apple-aspen-config" ||
+      // file.type might be empty on some systems as uncommon file extensions
+      // would return an empty string.
+      (file.type !== "" && file.type !== "application/x-apple-aspen-config") ||
       !file.name.includes(".mobileconfig")
     ) {
       renderFlash("error", UPLOAD_ERROR_MESSAGES.wrongType.message);