diff --git a/src/components/views/dialogs/InviteDialog.js b/src/components/views/dialogs/InviteDialog.js
index a2a0eddd8e..759228babd 100644
--- a/src/components/views/dialogs/InviteDialog.js
+++ b/src/components/views/dialogs/InviteDialog.js
@@ -577,8 +577,8 @@ export default class InviteDialog extends React.PureComponent {
         if (SettingsStore.getValue("feature_cross_signing")) {
             // Check whether all users have uploaded device keys before.
             // If so, enable encryption in the new room.
-            const containsNonMatrixUsers = targets.some(t => !(t instanceof DirectoryMember));
-            if (!containsNonMatrixUsers) {
+            const has3PidMembers = targets.some(t => t instanceof ThreepidMember);
+            if (has3PidMembers) {
                 const client = MatrixClientPeg.get();
                 const allHaveDeviceKeys = await canEncryptToAllUsers(client, targetIds);
                 if (allHaveDeviceKeys) {