diff --git a/openlp/core/common/registry.py b/openlp/core/common/registry.py
index 218325823..70c2fe3bd 100644
--- a/openlp/core/common/registry.py
+++ b/openlp/core/common/registry.py
@@ -105,7 +105,7 @@ class Registry(object):
         if key in self.service_list:
             del self.service_list[key]
 
-    def register_function(self, event, function):
+    def register_function(self, event, function, overwrite=False):
         """
         Register an event and associated function to be called
 
@@ -113,8 +113,9 @@ class Registry(object):
             will/may need to respond to a single action and the caller does not need to understand or know about the
             recipients.
         :param function: The function to be called when the event happens.
+        :param overwrite: There should only be one function with the registred name.
         """
-        if event in self.functions_list:
+        if not overwrite and event in self.functions_list:
             self.functions_list[event].append(function)
         else:
             self.functions_list[event] = [function]
diff --git a/openlp/core/ui/maindisplay.py b/openlp/core/ui/maindisplay.py
index f9f00a235..ceb94a2a9 100644
--- a/openlp/core/ui/maindisplay.py
+++ b/openlp/core/ui/maindisplay.py
@@ -153,9 +153,9 @@ class MainDisplay(OpenLPMixin, Display, RegistryProperties):
         self.setAttribute(QtCore.Qt.WA_DeleteOnClose)
         self.set_transparency(False)
         if self.is_live:
-            Registry().register_function('live_display_hide', self.hide_display)
-            Registry().register_function('live_display_show', self.show_display)
-            Registry().register_function('update_display_css', self.css_changed)
+            Registry().register_function('live_display_hide', self.hide_display, True)
+            Registry().register_function('live_display_show', self.show_display, True)
+            Registry().register_function('update_display_css', self.css_changed, True)
 
     def set_transparency(self, enabled):
         """