diff --git a/lib/types/identity-service-types.js b/lib/types/identity-service-types.js
--- a/lib/types/identity-service-types.js
+++ b/lib/types/identity-service-types.js
@@ -224,10 +224,18 @@
 export type SignedDeviceList = {
   // JSON-stringified RawDeviceList
   +rawDeviceList: string,
+  // Current primary device signature. Absent for Identity Service generated
+  // device lists.
+  +curPrimarySignature?: string,
+  // Previous primary device signature. Present only if primary device
+  // has changed since last update.
+  +lastPrimarySignature?: string,
 };
 export const signedDeviceListValidator: TInterface<SignedDeviceList> =
   tShape<SignedDeviceList>({
     rawDeviceList: t.String,
+    curPrimarySignature: t.maybe(t.String),
+    lastPrimarySignature: t.maybe(t.String),
   });
 export const signedDeviceListHistoryValidator: TList<Array<SignedDeviceList>> =
   t.list(signedDeviceListValidator);