diff --git a/templates/zephyr/index.html b/templates/zephyr/index.html
index dc7d06eab6..9df72a8087 100644
--- a/templates/zephyr/index.html
+++ b/templates/zephyr/index.html
@@ -45,7 +45,6 @@
 <script type="text/javascript">
 var initial_pointer = {{ user_profile.pointer }};
 var email = "{{ user_profile.user.email }}";
-// class_list only contains lower-case names.
 var class_list = {{ classes }};
 var people_list = {{ people }};
 var have_initial_messages = {{ have_initial_messages }};
diff --git a/tools/jslint/check-all.js b/tools/jslint/check-all.js
index 603b7e373b..de02038075 100644
--- a/tools/jslint/check-all.js
+++ b/tools/jslint/check-all.js
@@ -28,7 +28,8 @@ var globals =
     + ' loading_spinner templates'
 
     // subscribe.js
-    + ' fetch_subs sub_from_home'
+    + ' fetch_subs sub_from_home subscribed_to class_list_hash'
+    + ' add_to_class_list'
 
     // ui.js
     + ' register_onclick hide_email show_email'
diff --git a/zephyr/static/js/compose.js b/zephyr/static/js/compose.js
index 155244c6ca..3a4e258a31 100644
--- a/zephyr/static/js/compose.js
+++ b/zephyr/static/js/compose.js
@@ -124,7 +124,7 @@ function validate_class_message() {
     if (!check_class_for_send(class_name))
         return false;
 
-    if (class_list.indexOf(class_name.toLowerCase()) === -1) {
+    if (!subscribed_to(class_name)) {
         // You're not subbed to the class
         $('#send-status').removeClass(status_classes).show();
         $('#class-nosub-name').text(class_name);
diff --git a/zephyr/static/js/subscribe.js b/zephyr/static/js/subscribe.js
index 4858a5dc78..769e125fd5 100644
--- a/zephyr/static/js/subscribe.js
+++ b/zephyr/static/js/subscribe.js
@@ -26,7 +26,8 @@ function sub_from_home(zephyr_class, prompt_button) {
         data:      {new_subscription: zephyr_class},
         dataType: 'json',
         timeout:  10*60*1000, // 10 minutes in ms
-        success: function (data) {
+        success: function (response) {
+            add_to_class_list(response.data);
             $("#zephyr_compose form").ajaxSubmit();
             prompt_button.stop(true).fadeOut(500);
         },
@@ -36,6 +37,39 @@ function sub_from_home(zephyr_class, prompt_button) {
     });
 }
 
+class_list_hash = [];
+
+function subscribed_to(class_name) {
+    return (class_list_hash[class_name.toLowerCase()] === true);
+}
+
+function case_insensitive_subscription_index(class_name) {
+    var i;
+    var name = class_name.toLowerCase();
+
+    for (i = 1; i < class_list.length; i++) {
+        if (name === class_list[i].toLowerCase()) {
+            return i;
+        }
+    }
+    return -1;
+}
+
+function add_to_class_list(class_name) {
+    if (!subscribed_to(class_name)) {
+        class_list.push(class_name);
+        class_list_hash[class_name.toLowerCase()] = true;
+    }
+}
+
+function remove_from_class_list(class_name) {
+    delete class_list_hash[class_name.toLowerCase()];
+    var removal_index = case_insensitive_subscription_index(class_name);
+    if (removal_index !== -1) {
+        class_list.splice(removal_index, 1);
+    }
+}
+
 // FIXME: It would be nice to move the UI setup into ui.js.
 $(function () {
     $("#current_subscriptions").ajaxForm({
@@ -43,10 +77,7 @@ $(function () {
         success: function (resp, statusText, xhr, form) {
             var name = $.parseJSON(xhr.responseText).data;
             $('#subscriptions_table').find('button[value="' + name + '"]').parents('tr').remove();
-            var removal_index = class_list.indexOf(name.toLowerCase());
-            if (removal_index !== -1) {
-                class_list.splice(removal_index, 1);
-            }
+            remove_from_class_list(name);
             update_autocomplete();
             report_success("Successfully removed subscription to " + name,
                            $("#subscriptions-status"));
@@ -62,7 +93,7 @@ $(function () {
             $("#new_subscription").val("");
             var name = $.parseJSON(xhr.responseText).data;
             $('#subscriptions_table').prepend(templates.subscription({subscription: name}));
-            class_list.push(name.toLowerCase());
+            add_to_class_list(name);
             report_success("Successfully added subscription to " + name,
                            $("#subscriptions-status"));
             $("#new_subscription").focus();
diff --git a/zephyr/static/js/zephyr.js b/zephyr/static/js/zephyr.js
index 28e6a9d372..f0d2794b44 100644
--- a/zephyr/static/js/zephyr.js
+++ b/zephyr/static/js/zephyr.js
@@ -3,6 +3,7 @@ var zephyr_dict = {};
 var instance_list = [];
 
 $(function () {
+    var i;
     var send_status = $('#send-status');
     var buttons = $('#zephyr_compose').find('input[type="submit"]');
 
@@ -36,6 +37,11 @@ $(function () {
 
     send_status.hide();
     $("#zephyr_compose form").ajaxForm(options);
+
+    // Populate class_list_hash with data handed over to client-side template.
+    for (i = 0; i < class_list.length; i++) {
+        class_list_hash[class_list[i].toLowerCase()] = true;
+    }
 });
 
 var selected_zephyr_id = -1;  /* to be filled in on document.ready */
@@ -360,10 +366,6 @@ function add_zephyr_metadata(dummy, zephyr) {
     switch (zephyr.type) {
     case 'class':
         zephyr.is_class = true;
-        if ($.inArray(zephyr.display_recipient.toLowerCase(), class_list) === -1) {
-            class_list.push(zephyr.display_recipient.toLowerCase());
-            autocomplete_needs_update = true;
-        }
         if ($.inArray(zephyr.instance, instance_list) === -1) {
             instance_list.push(zephyr.instance);
             autocomplete_needs_update = true;