diff --git a/synapse/util/__init__.py b/synapse/util/__init__.py
index b3f76428b6..a3a75a292d 100644
--- a/synapse/util/__init__.py
+++ b/synapse/util/__init__.py
@@ -32,6 +32,7 @@ json_encoder = json.JSONEncoder(separators=(",", ":"))
 def unwrapFirstError(failure):
     # defer.gatherResults and DeferredLists wrap failures.
     failure.trap(defer.FirstError)
+    logger.info("DDD failure.value.subFailure: %s", failure.value.subFailure)
     return failure.value.subFailure