diff --git a/plugins/ContentFilter/ContentFilterPlugin.py b/plugins/ContentFilter/ContentFilterPlugin.py
index f46321d4..da1054b1 100644
--- a/plugins/ContentFilter/ContentFilterPlugin.py
+++ b/plugins/ContentFilter/ContentFilterPlugin.py
@@ -25,6 +25,13 @@ class SiteManagerPlugin(object):
         super(SiteManagerPlugin, self).load(*args, **kwargs)
         filter_storage = ContentFilterStorage(site_manager=self)
 
+    def add(self, address, *args, **kwargs):
+        if filter_storage.isSiteblocked(address):
+            details = filter_storage.getSiteblockDetails(address)
+            raise Exception("Site blocked: %s" % html.escape(details.get("reason", "unknown reason")))
+        else:
+            return super(SiteManagerPlugin, self).add(address, *args, **kwargs)
+
 
 @PluginManager.registerTo("UiWebsocket")
 class UiWebsocketPlugin(object):
diff --git a/plugins/ContentFilter/ContentFilterStorage.py b/plugins/ContentFilter/ContentFilterStorage.py
index 3df0b435..2215ccca 100644
--- a/plugins/ContentFilter/ContentFilterStorage.py
+++ b/plugins/ContentFilter/ContentFilterStorage.py
@@ -120,6 +120,12 @@ class ContentFilterStorage(object):
         else:
             return False
 
+    def getSiteblockDetails(self, address):
+        details = self.file_content["siteblocks"].get(address)
+        if not details:
+            details = self.include_filters["siteblocks"].get(address)
+        return details
+
     # Search and remove or readd files of an user
     def changeDbs(self, auth_address, action):
         self.log.debug("Mute action %s on user %s" % (action, auth_address))
diff --git a/plugins/MergerSite/MergerSitePlugin.py b/plugins/MergerSite/MergerSitePlugin.py
index ae2b1484..ca2ba31e 100644
--- a/plugins/MergerSite/MergerSitePlugin.py
+++ b/plugins/MergerSite/MergerSitePlugin.py
@@ -79,8 +79,11 @@ class UiWebsocketPlugin(object):
     def cbMergerSiteAdd(self, to, addresses):
         added = 0
         for address in addresses:
-            added += 1
-            site_manager.need(address)
+            try:
+                site_manager.need(address)
+                added += 1
+            except Exception as err:
+                self.cmd("notification", ["error", _["Adding <b>%s</b> failed: %s"] % (address, err)])
         if added:
             self.cmd("notification", ["done", _["Added <b>%s</b> new site"] % added, 5000])
         RateLimit.called(self.site.address + "-MergerSiteAdd")