diff --git a/schema.graphqls b/schema.graphqls
index b606eb8..6296660 100644
--- a/schema.graphqls
+++ b/schema.graphqls
@@ -67,8 +67,8 @@ type Query {
 
 # Mutations
 type Mutation {
-  scheduleNotification(input: NotificationInput!): NotificationResponse
-  cancelNotification(input: NotificationInput!): NotificationResponse
+  scheduleNotification(input: NotificationInput!): NotificationResponse!
+  cancelNotification(input: NotificationInput!): NotificationResponse!
 }
 
 input NotificationInput {