diff --git a/relay/application.py b/relay/application.py
index ee5b465..cb32357 100644
--- a/relay/application.py
+++ b/relay/application.py
@@ -262,7 +262,7 @@ class CachedStaticResource(StaticResource):
 		try:
 			return web.Response(
 				body = self.cache[rel_url],
-				content_type = guess_type(path)[0]
+				content_type = guess_type(rel_url)[0]
 			)
 
 		except KeyError: