diff --git a/src/stores/widgets/StopGapWidget.ts b/src/stores/widgets/StopGapWidget.ts
index 3b0a49f81836..c7eae0a57406 100644
--- a/src/stores/widgets/StopGapWidget.ts
+++ b/src/stores/widgets/StopGapWidget.ts
@@ -221,6 +221,7 @@ export class StopGapWidget extends EventEmitter {
             clientId: ELEMENT_CLIENT_ID,
             clientTheme: SettingsStore.getValue("theme"),
             clientLanguage: getUserLanguage(),
+            deviceId: this.client.getDeviceId(),
         };
         const templated = this.mockWidget.getCompleteUrl(Object.assign(defaults, fromCustomisation), opts?.asPopout);
 
diff --git a/test/stores/widgets/StopGapWidget-test.ts b/test/stores/widgets/StopGapWidget-test.ts
index 38e9983d49bd..da7612a3bf1c 100644
--- a/test/stores/widgets/StopGapWidget-test.ts
+++ b/test/stores/widgets/StopGapWidget-test.ts
@@ -42,7 +42,7 @@ describe("StopGapWidget", () => {
                 id: "test",
                 creatorUserId: "@alice:example.org",
                 type: "example",
-                url: "https://example.org",
+                url: "https://example.org?user-id=$matrix_user_id&device-id=$org.matrix.msc3819.device_id",
                 roomId: "!1:example.org",
             },
             room: mkRoom(client, "!1:example.org"),
@@ -60,6 +60,12 @@ describe("StopGapWidget", () => {
         widget.stopMessaging();
     });
 
+    it("should replace parameters in widget url template", () => {
+        expect(widget.embedUrl).toBe(
+            "https://example.org/?user-id=%40userId%3Amatrix.org&device-id=ABCDEFGHI&widgetId=test&parentUrl=http%3A%2F%2Flocalhost%2F",
+        );
+    });
+
     it("feeds incoming to-device messages to the widget", async () => {
         const event = mkEvent({
             event: true,