diff --git a/synapse/rest/well_known.py b/synapse/rest/well_known.py
index b8b4b5379b82..5f40c87c1123 100644
--- a/synapse/rest/well_known.py
+++ b/synapse/rest/well_known.py
@@ -43,6 +43,9 @@ def get_well_known(self) -> Optional[JsonDict]:
             result["m.identity_server"] = {
                 "base_url": self._config.registration.default_identity_server
             }
+        else:
+            # Workaround for iOS expecting some value here
+            result["m.identity_server"] = {"base_url": ""}
 
         # We use the MSC3861 values as they are used by multiple MSCs
         if self._config.experimental.msc3861.enabled: