diff --git a/src/components/views/right_panel/RoomHeaderButtons.tsx b/src/components/views/right_panel/RoomHeaderButtons.tsx
index d7f0af13b6e0..668ba2bdea80 100644
--- a/src/components/views/right_panel/RoomHeaderButtons.tsx
+++ b/src/components/views/right_panel/RoomHeaderButtons.tsx
@@ -44,6 +44,7 @@ import { NotificationStateEvents } from "../../../stores/notifications/Notificat
 import PosthogTrackers from "../../../PosthogTrackers";
 import { ButtonEvent } from "../elements/AccessibleButton";
 import { MatrixClientPeg } from "../../../MatrixClientPeg";
+import { doesRoomOrThreadHaveUnreadMessages } from "../../../Unread";
 
 const ROOM_INFO_PHASES = [
     RightPanelPhases.RoomSummary,
@@ -191,9 +192,17 @@ export default class RoomHeaderButtons extends HeaderButtons<IProps> {
                 return NotificationColor.Red;
             case NotificationCountType.Total:
                 return NotificationColor.Grey;
-            default:
-                return NotificationColor.None;
         }
+        // We don't have any notified messages, but we might have unread messages. Let's
+        // find out.
+        for (const thread of this.props.room!.getThreads()) {
+            // If the current thread has unread messages, we're done.
+            if (doesRoomOrThreadHaveUnreadMessages(thread)) {
+                return NotificationColor.Bold;
+            }
+        }
+        // Otherwise, no notification color.
+        return NotificationColor.None;
     }
 
     private onUpdateStatus = (notificationState: SummarizedNotificationState): void => {
diff --git a/test/components/views/right_panel/RoomHeaderButtons-test.tsx b/test/components/views/right_panel/RoomHeaderButtons-test.tsx
index f9a3572aa821..76118d6ad385 100644
--- a/test/components/views/right_panel/RoomHeaderButtons-test.tsx
+++ b/test/components/views/right_panel/RoomHeaderButtons-test.tsx
@@ -24,6 +24,7 @@ import RoomHeaderButtons from "../../../../src/components/views/right_panel/Room
 import { MatrixClientPeg } from "../../../../src/MatrixClientPeg";
 import SettingsStore from "../../../../src/settings/SettingsStore";
 import { stubClient } from "../../../test-utils";
+import { mkThread } from "../../../test-utils/threads";
 
 describe("RoomHeaderButtons-test.tsx", function () {
     const ROOM_ID = "!roomId:example.org";
@@ -52,7 +53,7 @@ describe("RoomHeaderButtons-test.tsx", function () {
         return container.querySelector(".mx_RightPanel_threadsButton");
     }
 
-    function isIndicatorOfType(container, type: "red" | "gray") {
+    function isIndicatorOfType(container, type: "red" | "gray" | "bold") {
         return container.querySelector(".mx_RightPanel_threadsButton .mx_Indicator").className.includes(type);
     }
 
@@ -76,7 +77,7 @@ describe("RoomHeaderButtons-test.tsx", function () {
         expect(container.querySelector(".mx_RightPanel_threadsButton .mx_Indicator")).toBeNull();
     });
 
-    it("room wide notification does not change the thread button", () => {
+    it("thread notification does change the thread button", () => {
         const { container } = getComponent(room);
 
         room.setThreadUnreadNotificationCount("$123", NotificationCountType.Total, 1);
@@ -89,6 +90,10 @@ describe("RoomHeaderButtons-test.tsx", function () {
         room.setThreadUnreadNotificationCount("$123", NotificationCountType.Highlight, 0);
 
         expect(container.querySelector(".mx_RightPanel_threadsButton .mx_Indicator")).toBeNull();
+
+        // Thread activity should appear on the icon.
+        mkThread({ room, client, authorId: client.getUserId()!, participantUserIds: ["@alice:example.org"] });
+        expect(isIndicatorOfType(getComponent(room), "bold")).toBe(true);
     });
 
     it("does not explode without a room", () => {