diff --git a/ui/src/views/Tasks/submitTaskAction.js b/ui/src/views/Tasks/submitTaskAction.js
index 05f01e885cd..496fc71d1a4 100644
--- a/ui/src/views/Tasks/submitTaskAction.js
+++ b/ui/src/views/Tasks/submitTaskAction.js
@@ -13,7 +13,18 @@ import ajv from '../../utils/ajv';
 
 export default async ({ task, form, action, apolloClient, taskActions }) => {
   const actions = removeKeys(cloneDeep(taskActions), ['__typename']);
-  const taskGroup = task.taskId === task.taskGroupId ? task : task.decisionTask;
+  // We need to source scopes from somewhere. Typically these come from the task we're given,
+  // which is either a regular decision task or an action task. Decision tasks are easily
+  // identified, because their taskId matches the taskGroupId that they are in. Action tasks
+  // do not have such a mapping. Instead, we're simply going to try our best by falling back
+  // to `task` if `task.decisionTask` is null or undefined.
+  // At the time of writing, it's not clear whether the `task.decisionTask` case is even valid
+  // anymore, but it's being kept for the time being because verifying that is not a trivial
+  // matter.
+  const taskGroup =
+    task.taskId === task.taskGroupId || !task.decisionTask
+      ? task
+      : task.decisionTask;
   const input = load(form);
   const validate = ajv.compile(action.schema || {});
   const valid = validate(input);