diff --git a/src/components/structures/MatrixChat.js b/src/components/structures/MatrixChat.js
index af3f4d2598..2515035996 100644
--- a/src/components/structures/MatrixChat.js
+++ b/src/components/structures/MatrixChat.js
@@ -1505,6 +1505,15 @@ export default createReactClass({
                 "blacklistUnverifiedDevices",
             );
             cli.setGlobalBlacklistUnverifiedDevices(blacklistEnabled);
+
+            // With cross-signing enabled, we send to unknown devices
+            // without prompting. Any bad-device status the user should
+            // be aware of will be signalled through the room shield
+            // changing colour. More advanced behaviour will come once
+            // we implement more settings.
+            cli.setGlobalErrorOnUnknownDevices(
+                !SettingsStore.isFeatureEnabled("feature_cross_signing"),
+            );
         }
     },