diff --git a/static/js/referral.js b/static/js/referral.js
index ef88ea7bcb..3f76a0ab54 100644
--- a/static/js/referral.js
+++ b/static/js/referral.js
@@ -54,6 +54,7 @@ exports.update_state = function (granted, used) {
             $(".no-more-invites").hide();
         } else {
             $(".still-have-invites").hide();
+            $("#referral-form input").blur();
             if (ever_had_invites) {
                 $(".no-more-invites").show();
             }
diff --git a/templates/zerver/left-sidebar.html b/templates/zerver/left-sidebar.html
index 1d52d4370b..7ac000bbdc 100644
--- a/templates/zerver/left-sidebar.html
+++ b/templates/zerver/left-sidebar.html
@@ -43,7 +43,7 @@
                         <div class="still-have-invites">
                           {#  Many of these values are set by the initialization code in referral.js  #}
                           <form id="referral-form">
-                            <input class="input-block-level" type="email" name="email" />
+                            <input class="input-block-level required" type="email" name="email" />
                           </form>
                         </div>
                         <div class="invite-count-area">
diff --git a/zerver/views.py b/zerver/views.py
index fa0d6f0a3d..856f4d3225 100644
--- a/zerver/views.py
+++ b/zerver/views.py
@@ -2223,6 +2223,8 @@ def json_get_bots(request, user_profile):
 @authenticated_json_post_view
 @has_request_variables
 def json_refer_friend(request, user_profile, email=REQ):
+    if not email:
+        return json_error("No email address specified")
     if user_profile.invites_granted - user_profile.invites_used <= 0:
         return json_error("Insufficient invites")