diff --git a/synapse/http/server.py b/synapse/http/server.py
index 66f966fcaa3c43adab94a431d75ccba9ceda0f5b..243b71744d12b3d041beb5baa54036d2e908c6ea 100644
--- a/synapse/http/server.py
+++ b/synapse/http/server.py
@@ -325,7 +325,7 @@ class ContentRepoResource(resource.Resource):
 
             # FIXME (erikj): These should use constants.
             file_name = os.path.basename(fname)
-            url = "http://%s/matrix/content/%s" % (
+            url = "http://%s/_matrix/content/%s" % (
                 self.hs.domain_with_port, file_name
             )