--- a/taskcluster/taskgraph/decision.py
+++ b/taskcluster/taskgraph/decision.py
@@ -36,16 +36,17 @@ PER_PROJECT_PARAMETERS = {
         # we submit decision tasks against Try that use other
         # `target_task_method`s, like `nightly_fennec` or `mozilla_beta_tasks`,
         # which reference the `include_nightly` parameter.
         'include_nightly': True,
     },
 
     'try-comm-central': {
         'target_tasks_method': 'try_tasks',
+        'include_nightly': True,
     },
 
     'ash': {
         'target_tasks_method': 'ash_tasks',
         'optimize_target_tasks': True,
         'include_nightly': False,
     },
 
@@ -237,17 +238,19 @@ def get_decision_parameters(options):
             # process to all of the tasks.
             parameters['optimize_target_tasks'] = True
 
     else:
         parameters['try_mode'] = None
         parameters['try_task_config'] = None
         parameters['try_options'] = None
 
-    return Parameters(**parameters)
+    result = Parameters(**parameters)
+    result.check()
+    return result
 
 
 def write_artifact(filename, data):
     logger.info('writing artifact file `{}`'.format(filename))
     if not os.path.isdir(ARTIFACTS_DIR):
         os.mkdir(ARTIFACTS_DIR)
     path = os.path.join(ARTIFACTS_DIR, filename)
     if filename.endswith('.yml'):