diff --git a/src/stores/widgets/StopGapWidgetDriver.ts b/src/stores/widgets/StopGapWidgetDriver.ts
index 248c520ddd5..f6bffca3d29 100644
--- a/src/stores/widgets/StopGapWidgetDriver.ts
+++ b/src/stores/widgets/StopGapWidgetDriver.ts
@@ -144,13 +144,31 @@ export class StopGapWidgetDriver extends WidgetDriver {
             this.allowedCapabilities.add(
                 WidgetEventCapability.forStateEvent(EventDirection.Receive, EventType.RoomEncryption).raw,
             );
+            const clientUserId = MatrixClientPeg.safeGet().getSafeUserId();
+            // For the legacy membership type
             this.allowedCapabilities.add(
-                WidgetEventCapability.forStateEvent(
-                    EventDirection.Send,
-                    "org.matrix.msc3401.call.member",
-                    MatrixClientPeg.safeGet().getSafeUserId(),
-                ).raw,
+                WidgetEventCapability.forStateEvent(EventDirection.Send, "org.matrix.msc3401.call.member", clientUserId)
+                    .raw,
             );
+            const clientDeviceId = MatrixClientPeg.safeGet().getDeviceId();
+            if (clientDeviceId !== null) {
+                // For the session membership type compliant with MSC4143
+                this.allowedCapabilities.add(
+                    WidgetEventCapability.forStateEvent(
+                        EventDirection.Send,
+                        "org.matrix.msc3401.call.member",
+                        `_${clientUserId}_${clientDeviceId}`,
+                    ).raw,
+                );
+                // MSC3779 version, with no leading underscore
+                this.allowedCapabilities.add(
+                    WidgetEventCapability.forStateEvent(
+                        EventDirection.Send,
+                        "org.matrix.msc3401.call.member",
+                        `${clientUserId}_${clientDeviceId}`,
+                    ).raw,
+                );
+            }
             this.allowedCapabilities.add(
                 WidgetEventCapability.forStateEvent(EventDirection.Receive, "org.matrix.msc3401.call.member").raw,
             );
diff --git a/test/stores/widgets/StopGapWidgetDriver-test.ts b/test/stores/widgets/StopGapWidgetDriver-test.ts
index 6e51d4ae980..5ba95d901dd 100644
--- a/test/stores/widgets/StopGapWidgetDriver-test.ts
+++ b/test/stores/widgets/StopGapWidgetDriver-test.ts
@@ -99,6 +99,8 @@ describe("StopGapWidgetDriver", () => {
             "org.matrix.msc2762.receive.state_event:org.matrix.msc3401.call",
             "org.matrix.msc2762.send.state_event:org.matrix.msc3401.call.member#@alice:example.org",
             "org.matrix.msc2762.receive.state_event:org.matrix.msc3401.call.member",
+            `org.matrix.msc2762.send.state_event:org.matrix.msc3401.call.member#_@alice:example.org_${client.deviceId}`,
+            `org.matrix.msc2762.send.state_event:org.matrix.msc3401.call.member#@alice:example.org_${client.deviceId}`,
             "org.matrix.msc3819.send.to_device:m.call.invite",
             "org.matrix.msc3819.receive.to_device:m.call.invite",
             "org.matrix.msc3819.send.to_device:m.call.candidates",