diff --git a/cylc/flow/network/schema.py b/cylc/flow/network/schema.py
index 971e63c25f8..f2d42bd729f 100644
--- a/cylc/flow/network/schema.py
+++ b/cylc/flow/network/schema.py
@@ -1410,6 +1410,7 @@ class Flow(String):
     """An integer or one of {FLOW_ALL}, {FLOW_NEW} or {FLOW_NONE}."""
     # (Note docstrings can't be f-strings).
 
+
 # Mutations:
 
 # TODO: re-instate:
diff --git a/cylc/flow/scripts/trigger.py b/cylc/flow/scripts/trigger.py
index c1b554f2bbb..0c013fc4072 100755
--- a/cylc/flow/scripts/trigger.py
+++ b/cylc/flow/scripts/trigger.py
@@ -69,7 +69,7 @@
 mutation (
   $wFlows: [WorkflowID]!,
   $tasks: [NamespaceIDGlob]!,
-  $flow: [String],
+  $flow: [Flow!],
   $flowWait: Boolean,
   $flowDescr: String,
 ) {