diff --git a/static/js/ui.js b/static/js/ui.js
index ce4ccdd91e..df2083b798 100644
--- a/static/js/ui.js
+++ b/static/js/ui.js
@@ -46,6 +46,20 @@ function update_message_in_all_views(message_id, callback) {
     });
 }
 
+exports.show_error_for_unsupported_platform = function () {
+    if (/ZulipDesktop/.test(navigator.userAgent)) {
+        // We don't internationalize this string because it is long,
+        // and few users will have both the old desktop app and an
+        // internationalized version of Zulip anyway.
+        var error = "Hello! You're using the unsupported old Zulip desktop app," +
+            " which is no longer developed. We recommend switching to the new, " +
+            "modern desktop app, which you can download at " +
+            "<a href='https://zulipchat.com/apps'>zulipchat.com/apps</a>.";
+
+        ui_report.generic_embed_error(error);
+    }
+};
+
 exports.find_message = function (message_id) {
     // Try to find the message object. It might be in the narrow list
     // (if it was loaded when narrowed), or only in the message_list.all
@@ -285,6 +299,7 @@ $(function () {
 
 exports.initialize = function () {
     i18n.ensure_i18n(_setup_info_overlay);
+    exports.show_error_for_unsupported_platform();
 };
 
 return exports;
diff --git a/static/js/ui_report.js b/static/js/ui_report.js
index 251c7be183..dfe62b4138 100644
--- a/static/js/ui_report.js
+++ b/static/js/ui_report.js
@@ -43,6 +43,13 @@ exports.success = function (response, status_box, type) {
     exports.message(response, status_box, 'alert-success', type);
 };
 
+exports.generic_embed_error = function (error) {
+    var $alert = $("<div class='alert home-error-bar'></div>");
+    var $exit = "<div class='exit'></div>";
+
+    $(".alert-box").append($alert.html($exit + "<div class='content'>" + error + "</div>").addClass("show"));
+};
+
 exports.hide_error = function ($target) {
     $target.addClass("fade-out");
     setTimeout(function () {