diff --git a/frontend_tests/node_tests/unread.js b/frontend_tests/node_tests/unread.js
index 8f808d799a..34ceefff47 100644
--- a/frontend_tests/node_tests/unread.js
+++ b/frontend_tests/node_tests/unread.js
@@ -319,8 +319,8 @@ var zero_counts = {
     };
     people.add_in_realm(bob);
 
-    assert.equal(unread.num_unread_for_person('alice@example.com'), 0);
-    assert.equal(unread.num_unread_for_person('bob@example.com'), 0);
+    assert.equal(unread.num_unread_for_person(alice.user_id), 0);
+    assert.equal(unread.num_unread_for_person(bob.user_id), 0);
 
     var message = {
         id: 15,
@@ -332,7 +332,7 @@ var zero_counts = {
         flags: ['read']
     };
     unread.process_loaded_messages([message, read_message]);
-    assert.equal(unread.num_unread_for_person('alice@example.com'), 1);
+    assert.equal(unread.num_unread_for_person(alice.user_id), 1);
 }());
 
 
diff --git a/static/js/activity.js b/static/js/activity.js
index f9f7a03186..700aa6cff7 100644
--- a/static/js/activity.js
+++ b/static/js/activity.js
@@ -277,11 +277,11 @@ exports.update_users = function (user_list) {
     }
     users = filter_and_sort(users);
 
-    function get_num_unread(email) {
+    function get_num_unread(user_id) {
         if (unread.suppress_unread_counts) {
             return 0;
         }
-        return unread.num_unread_for_person(email);
+        return unread.num_unread_for_person(user_id);
     }
 
     // Note that we do not include ourselves in the user list any more.
@@ -291,11 +291,10 @@ exports.update_users = function (user_list) {
     function info_for(user_id) {
         var presence = exports.presence_info[user_id].status;
         var person = people.get_person_from_user_id(user_id);
-        var email = person.email;
         return {
             name: person.full_name,
             user_id: user_id,
-            num_unread: get_num_unread(email),
+            num_unread: get_num_unread(user_id),
             type: presence,
             type_desc: presence_descriptions[presence],
             mobile: exports.presence_info[user_id].mobile
@@ -361,8 +360,7 @@ exports.update_huddles = function () {
     $('#group-pms').expectOne().html(html);
 
     _.each(huddles, function (user_ids_string) {
-        var emails_string = people.user_ids_string_to_emails_string(user_ids_string);
-        var count = unread.num_unread_for_person(emails_string);
+        var count = unread.num_unread_for_person(user_ids_string);
         set_count(user_ids_string, count);
     });
 
diff --git a/static/js/pm_list.js b/static/js/pm_list.js
index df24a77298..9ab25aa76c 100644
--- a/static/js/pm_list.js
+++ b/static/js/pm_list.js
@@ -84,7 +84,7 @@ exports._build_private_messages_list = function (active_conversation, max_privat
         var user_ids_string = private_message_obj.user_ids_string;
         var reply_to = people.user_ids_string_to_emails_string(user_ids_string);
 
-        var num_unread = unread.num_unread_for_person(reply_to);
+        var num_unread = unread.num_unread_for_person(user_ids_string);
 
         var always_visible = (idx < max_private_messages) || (num_unread > 0)
             || (user_ids_string === active_conversation);
diff --git a/static/js/unread.js b/static/js/unread.js
index 284cf1e609..c717e26e2d 100644
--- a/static/js/unread.js
+++ b/static/js/unread.js
@@ -174,8 +174,7 @@ exports.num_unread_for_subject = function (stream, subject) {
     return num_unread;
 };
 
-exports.num_unread_for_person = function (emails_string) {
-    var user_ids_string = people.emails_strings_to_user_ids_string(emails_string);
+exports.num_unread_for_person = function (user_ids_string) {
     if (!user_ids_string) {
         return 0;
     }