diff --git a/chat_box/views.py b/chat_box/views.py
index a20bb0a..e472b56 100644
--- a/chat_box/views.py
+++ b/chat_box/views.py
@@ -182,20 +182,21 @@ def check_valid_message(request, room):
         return False
 
     try:
-        last_msg_all = Message.objects.filter(room=room).latest("time")
+        last_msg = Message.objects.filter(room=room).first()
+        if (
+            last_msg.author == request.profile
+            and last_msg.body == request.POST["body"].strip()
+        ):
+            return False
     except Message.DoesNotExist:
-        last_msg_all = None
-
-    if last_msg_all and last_msg_all.body == request.POST["body"].strip():
-        return False
+        pass
 
     if not room:
-        four_last_msg = Message.objects.filter(
-            author=request.profile, room=room
-        ).order_by("-time")[:4]
+        four_last_msg = Message.objects.filter(room=room).order_by("-id")[:4]
         if len(four_last_msg) >= 4:
+            same_author = all(msg.author == request.profile for msg in four_last_msg)
             time_diff = timezone.now() - four_last_msg[3].time
-            if time_diff.total_seconds() < 15:
+            if same_author and time_diff.total_seconds() < 300:
                 return False
 
     return True
@@ -207,7 +208,7 @@ def post_message(request):
 
     if request.method != "POST":
         return HttpResponseBadRequest()
-    if len(request.POST["body"]) > 5000:
+    if len(request.POST["body"]) > 5000 or len(request.POST["body"].strip()) == 0:
         return HttpResponseBadRequest()
 
     room = None
diff --git a/templates/chat/chat_js.html b/templates/chat/chat_js.html
index ed61f89..e259b87 100644
--- a/templates/chat/chat_js.html
+++ b/templates/chat/chat_js.html
@@ -36,8 +36,7 @@
           $('#chat-log').prepend(data);
         }
 
-        register_time($('.time-with-rel'));
-        merge_authors();
+        postProcessMessages();
 
         if (!refresh_html) {
           $chat_box.scrollTop(scrollTopOfBottom($chat_box) - lastMsgPos);
@@ -51,6 +50,13 @@
     })
   }
 
+  function postProcessMessages() {
+    register_time($('.time-with-rel'));
+    MathJax.typeset();
+    populateCopyButton();
+    merge_authors();
+  }
+
   function scrollTopOfBottom(container) {
     return container[0].scrollHeight - container.innerHeight()
   }
@@ -111,10 +117,7 @@
 
     $('#chat-log').append($data);
     $('#chat-box').scrollTop($('#chat-box')[0].scrollHeight);
-    register_time($('.time-with-rel'));
-    MathJax.typeset();
-    populateCopyButton();
-    merge_authors();
+    postProcessMessages();
   }
 
   function add_new_message(message, room, is_self_author) {
@@ -167,11 +170,8 @@
           else {
             add_new_message(message, room, true);
           }
-          MathJax.typeset();
-          populateCopyButton();
-          register_time($('.time-with-rel'));
           remove_unread_current_user();
-          merge_authors();
+          postProcessMessages();
         },
         error: function (data) {
           console.log('Fail to check message');
@@ -310,8 +310,9 @@
       load_next_page(null, true);
       update_last_seen();
       refresh_status(true);
-      $('#chat-input').focus();
+
       show_right_panel();
+      $('#chat-input').focus();
       $('#chat-input').val('').trigger('input');
     }
     window.lock_click_space = true;