diff --git a/crc/scripts/start_workflow.py b/crc/scripts/start_workflow.py
index 1727298a..69737fad 100644
--- a/crc/scripts/start_workflow.py
+++ b/crc/scripts/start_workflow.py
@@ -63,8 +63,12 @@ class StartWorkflow(Script):
                 filter(WorkflowModel.workflow_spec_id==workflow_spec_id).\
                 first()
 
-            workflow_api = self.get_workflow(workflow.id)
-            return workflow_api
+            if workflow:
+                workflow_api = self.get_workflow(workflow.id)
+                return workflow_api
+            else:
+                raise ApiError(code='unknown_workflow',
+                               message=f"We could not find a workflow with workflow_spec_id '{workflow_spec_id}'.")
 
         else:
             raise ApiError(code='missing_parameter',
diff --git a/tests/scripts/test_start_workflow.py b/tests/scripts/test_start_workflow.py
index b4dfcf9f..4ca1ea09 100644
--- a/tests/scripts/test_start_workflow.py
+++ b/tests/scripts/test_start_workflow.py
@@ -9,12 +9,7 @@ from crc.services.workflow_spec_service import WorkflowSpecService
 
 class TestStartWorkflow(BaseTest):
 
-    def test_start_workflow_validation(self):
-        spec_model = self.load_test_spec('start_workflow')
-        rv = self.app.get('/v1.0/workflow-specification/%s/validate' % spec_model.id, headers=self.logged_in_headers())
-        self.assertEqual([], rv.json)
-
-    def test_start_workflow(self):
+    def setup_test_start_workflow(self):
         self.add_users()
         self.create_workflow('hello_world')
         workflow_spec_to_start = WorkflowSpecService().get_spec('hello_world')
@@ -24,6 +19,16 @@ class TestStartWorkflow(BaseTest):
         study = session.query(StudyModel).filter(StudyModel.id==study_id).first()
         StudyService.add_all_workflow_specs_to_study(study, [workflow_spec_to_start])
 
+        return workflow
+
+    def test_start_workflow_validation(self):
+        spec_model = self.load_test_spec('start_workflow')
+        rv = self.app.get('/v1.0/workflow-specification/%s/validate' % spec_model.id, headers=self.logged_in_headers())
+        self.assertEqual([], rv.json)
+
+    def test_start_workflow(self):
+        workflow = self.setup_test_start_workflow()
+
         workflow_before = session.query(WorkflowModel).filter(WorkflowModel.workflow_spec_id=='hello_world').first()
         self.assertEqual('not_started', workflow_before.status.value)
 
@@ -33,3 +38,10 @@ class TestStartWorkflow(BaseTest):
 
         workflow_after = session.query(WorkflowModel).filter(WorkflowModel.workflow_spec_id=='hello_world').first()
         self.assertEqual('user_input_required', workflow_after.status.value)
+
+    def test_bad_workflow_spec_id(self):
+        workflow = self.setup_test_start_workflow()
+        workflow_api = self.get_workflow_api(workflow)
+        task = workflow_api.next_task
+        with self.assertRaises(AssertionError) as e:
+            self.complete_form(workflow, task, {'workflow_spec_to_start': 'bad_spec_id'})