diff --git a/changelog.d/15614.bugfix b/changelog.d/15614.bugfix
new file mode 100644
index 000000000..b523ae6eb
--- /dev/null
+++ b/changelog.d/15614.bugfix
@@ -0,0 +1 @@
+Fix a bug introduced in Synapse 1.82.0 where the error message displayed when validation of the `app_service_config_files` config option fails would be incorrectly formatted.
diff --git a/synapse/config/appservice.py b/synapse/config/appservice.py
index fd89960e7..c2710fdf0 100644
--- a/synapse/config/appservice.py
+++ b/synapse/config/appservice.py
@@ -36,11 +36,10 @@ class AppServiceConfig(Config):
         if not isinstance(self.app_service_config_files, list) or not all(
             type(x) is str for x in self.app_service_config_files
         ):
-            # type-ignore: this function gets arbitrary json value; we do use this path.
             raise ConfigError(
                 "Expected '%s' to be a list of AS config files:"
                 % (self.app_service_config_files),
-                "app_service_config_files",
+                ("app_service_config_files",),
             )
 
         self.track_appservice_user_ips = config.get("track_appservice_user_ips", False)