1 files changed, 1 insertions, 1 deletions
diff --git a/synapse/handlers/cas.py b/synapse/handlers/cas.py
index b681d208bc..0325f86e20 100644
--- a/synapse/handlers/cas.py
+++ b/synapse/handlers/cas.py
@@ -40,7 +40,7 @@ class CasError(Exception):
 
     def __str__(self):
         if self.error_description:
-            return "{}: {}".format(self.error, self.error_description)
+            return f"{self.error}: {self.error_description}"
         return self.error