diff --git a/src/petab_gui/C.py b/src/petab_gui/C.py
index dfc8548..af2d7f8 100644
--- a/src/petab_gui/C.py
+++ b/src/petab_gui/C.py
@@ -34,7 +34,7 @@
     },
     "condition": {
         "conditionId": {"type": "STRING", "optional": False},
-        "conditionName": {"type": "STRING", "optional": True},
+        "conditionName": {"type": "STRING", "optional": False},
     }
     }