diff --git a/synapse/rest/media/v1/upload_resource.py b/synapse/rest/media/v1/upload_resource.py
index e73e431dc9f1..05966bf8b104 100644
--- a/synapse/rest/media/v1/upload_resource.py
+++ b/synapse/rest/media/v1/upload_resource.py
@@ -103,4 +103,6 @@ async def _async_render_POST(self, request: SynapseRequest) -> None:
 
         logger.info("Uploaded content with URI %r", content_uri)
 
-        respond_with_json(request, 200, {"content_uri": content_uri}, send_cors=True)
+        respond_with_json(
+            request, 200, {"content_uri": content_uri.to_string()}, send_cors=True
+        )