diff --git a/packages/trace-viewer/src/ui/sourceTab.tsx b/packages/trace-viewer/src/ui/sourceTab.tsx
index 50d96f8ee3..9e26bf13a9 100644
--- a/packages/trace-viewer/src/ui/sourceTab.tsx
+++ b/packages/trace-viewer/src/ui/sourceTab.tsx
@@ -67,7 +67,10 @@ export const SourceTab: React.FunctionComponent<{
         let response = await fetch(`sha1/src@${sha1}.txt`);
         if (response.status === 404)
           response = await fetch(`file?path=${encodeURIComponent(file)}`);
-        source.content = await response.text();
+        if (response.status >= 400)
+          source.content = `<Unable to read "${file}">`;
+        else
+          source.content = await response.text();
       } catch {
         source.content = `<Unable to read "${file}">`;
       }