diff --git a/frontend_tests/node_tests/narrow_unread.js b/frontend_tests/node_tests/narrow_unread.js
index 08c196d02a..4ec577ff69 100644
--- a/frontend_tests/node_tests/narrow_unread.js
+++ b/frontend_tests/node_tests/narrow_unread.js
@@ -47,6 +47,7 @@ function set_filter(terms) {
     set_filter(terms);
     unread_ids = narrow_state.get_unread_ids();
     assert.equal(unread_ids, undefined);
+    assert.equal(narrow_state.get_first_unread_id(), undefined);
 
     terms = [
         {operator: 'stream', operand: 'bogus'},
@@ -61,6 +62,7 @@ function set_filter(terms) {
     set_filter(terms);
     unread_ids = narrow_state.get_unread_ids();
     assert.deepEqual(unread_ids, []);
+    assert.equal(narrow_state.get_first_unread_id(), undefined);
 
     msg = {
         id: 101,
@@ -74,6 +76,7 @@ function set_filter(terms) {
 
     unread_ids = narrow_state.get_unread_ids();
     assert.deepEqual(unread_ids, [msg.id]);
+    assert.equal(narrow_state.get_first_unread_id(), msg.id);
 
     terms = [
         {operator: 'stream', operand: 'bogus'},
diff --git a/static/js/narrow_state.js b/static/js/narrow_state.js
index 9a54ebce10..9da9bfc19c 100644
--- a/static/js/narrow_state.js
+++ b/static/js/narrow_state.js
@@ -169,6 +169,21 @@ exports.pm_string = function () {
     return user_ids_string;
 };
 
+exports.get_first_unread_id = function () {
+    // This function may return undefined for two different
+    // reasons: we have no unread messages, or we don't have
+    // an easy, inexpensive way to calculate them.  See the
+    // comment in get_unread_ids() for more details.
+
+    var unread_ids = exports.get_unread_ids();
+
+    if (unread_ids === undefined) {
+        return;
+    }
+
+    return unread_ids[0];
+};
+
 exports.get_unread_ids = function () {
     // This function currently only returns valid results for
     // certain types of narrows, mostly left sidebar narrows.