diff --git a/keyserver/src/responders/user-responders.js b/keyserver/src/responders/user-responders.js
--- a/keyserver/src/responders/user-responders.js
+++ b/keyserver/src/responders/user-responders.js
@@ -189,7 +189,7 @@
   calendarQuery: t.maybe(entryQueryInputValidator),
   deviceTokenUpdateRequest: t.maybe(deviceTokenUpdateRequestInputValidator),
   platformDetails: tPlatformDetails,
-  source: t.maybe(t.enums.of(values(loginActionSources))),
+  source: t.enums.of(values(loginActionSources)),
 });
 
 async function logInResponder(
diff --git a/lib/types/account-types.js b/lib/types/account-types.js
--- a/lib/types/account-types.js
+++ b/lib/types/account-types.js
@@ -114,6 +114,7 @@
   +deviceTokenUpdateRequest?: ?DeviceTokenUpdateRequest,
   +platformDetails: PlatformDetails,
   +watchedIDs: $ReadOnlyArray<string>,
+  +source: LogInActionSource,
 };
 
 export type LogInResponse = {