1 files changed, 2 insertions, 1 deletions
diff --git a/synapse/rest/client/v2_alpha/register.py b/synapse/rest/client/v2_alpha/register.py
index 5d50dd9e3d..56a5bbec30 100644
--- a/synapse/rest/client/v2_alpha/register.py
+++ b/synapse/rest/client/v2_alpha/register.py
@@ -34,7 +34,8 @@ from synapse.util.async import run_on_reactor
 if hasattr(hmac, "compare_digest"):
     compare_digest = hmac.compare_digest
 else:
-    compare_digest = lambda a, b: a == b
+    def compare_digest(a, b):
+        return a == b
 
 
 logger = logging.getLogger(__name__)