diff --git a/frontend_tests/node_tests/filter.js b/frontend_tests/node_tests/filter.js
index eda55ed0b4..7583acd9c5 100644
--- a/frontend_tests/node_tests/filter.js
+++ b/frontend_tests/node_tests/filter.js
@@ -1478,6 +1478,9 @@ test("navbar_helpers", () => {
     const group_pm_including_missing_person = [
         {operator: "pm-with", operand: "joe@example.com,STEVE@foo.com,sally@doesnotexist.com"},
     ];
+    // not common narrows, but used for browser title updates
+    const is_alerted = [{operator: "is", operand: "alerted"}];
+    const is_unread = [{operator: "is", operand: "unread"}];
 
     const test_cases = [
         {
@@ -1598,6 +1601,20 @@ test("navbar_helpers", () => {
             ]),
             redirect_url_with_search: "/#narrow/pm-with/undefined",
         },
+        {
+            operator: is_alerted,
+            is_common_narrow: false,
+            icon: undefined,
+            title: "translated: Alerted messages",
+            redirect_url_with_search: "#",
+        },
+        {
+            operator: is_unread,
+            is_common_narrow: false,
+            icon: undefined,
+            title: "translated: Unread messages",
+            redirect_url_with_search: "#",
+        },
     ];
 
     for (const test_case of test_cases) {
diff --git a/static/js/filter.js b/static/js/filter.js
index ccc83320f1..ffb7e5c500 100644
--- a/static/js/filter.js
+++ b/static/js/filter.js
@@ -706,6 +706,13 @@ export class Filter {
                 }
                 case "is-resolved":
                     return $t({defaultMessage: "Topics marked as resolved"});
+                // These cases return false for is_common_narrow, and therefore are not
+                // formatted in the message view header. They are used in narrow.js to
+                // update the browser title.
+                case "is-alerted":
+                    return $t({defaultMessage: "Alerted messages"});
+                case "is-unread":
+                    return $t({defaultMessage: "Unread messages"});
             }
         }
         /* istanbul ignore next */