diff --git a/lib/shared/device-list-utils.js b/lib/shared/device-list-utils.js
--- a/lib/shared/device-list-utils.js
+++ b/lib/shared/device-list-utils.js
@@ -141,16 +141,12 @@
   deviceListPayload: RawDeviceList,
 ): Promise<SignedDeviceList> {
   const deviceID = await getContentSigningKey();
-  const rawDeviceList = JSON.stringify(deviceListPayload);
-
-  // don't sign device list if current device is not a primary one
   if (deviceListPayload.devices[0] !== deviceID) {
-    return {
-      rawDeviceList,
-    };
+    throw new Error('non-primary device tried to sign device list');
   }
 
   const { olmAPI } = getConfig();
+  const rawDeviceList = JSON.stringify(deviceListPayload);
   const curPrimarySignature = await olmAPI.signMessage(rawDeviceList);
   return {
     rawDeviceList,
diff --git a/lib/shared/device-list-utils.test.js b/lib/shared/device-list-utils.test.js
--- a/lib/shared/device-list-utils.test.js
+++ b/lib/shared/device-list-utils.test.js
@@ -169,7 +169,7 @@
 
 describe(addDeviceToDeviceList, () => {
   it('adds device to device list', async () => {
-    mockOlmAPISign();
+    mockOlmAPISign(defaultOlmAPISignMock, 'D1');
 
     const updates: $ReadOnlyArray<SignedDeviceList> = [
       createDeviceList({ devices: ['D1'], timestamp: 1 }),
@@ -197,7 +197,7 @@
 
 describe(removeDeviceFromDeviceList, () => {
   it('removes device from device list', async () => {
-    mockOlmAPISign();
+    mockOlmAPISign(defaultOlmAPISignMock, 'D1');
 
     const updates: $ReadOnlyArray<SignedDeviceList> = [
       createDeviceList({ devices: ['D1', 'D2'], timestamp: 1 }),