diff --git a/avocado/core/dispatcher.py b/avocado/core/dispatcher.py
index 1f7ab88fb2a39c46d44884faae2319e67ccb35d8..12a2026e0ae6f75714049e3bd9a01f6801f1bd0b 100644
--- a/avocado/core/dispatcher.py
+++ b/avocado/core/dispatcher.py
@@ -27,7 +27,8 @@ class Dispatcher(ExtensionManager):
         self.load_failures = []
         super(Dispatcher, self).__init__(namespace=namespace,
                                          invoke_on_load=True,
-                                         on_load_failure_callback=self.store_load_failure)
+                                         on_load_failure_callback=self.store_load_failure,
+                                         propagate_map_exceptions=True)
 
     @staticmethod
     def store_load_failure(manager, entrypoint, exception):
diff --git a/avocado/core/loader.py b/avocado/core/loader.py
index 5d6035e9eeb8541f3fd46b6867462be70fc482a1..e83916d884e08859202e701782e576789f87ab12 100644
--- a/avocado/core/loader.py
+++ b/avocado/core/loader.py
@@ -102,7 +102,8 @@ class TestLoaderProxy(object):
     def register_plugin(self, plugin):
         try:
             if issubclass(plugin, TestLoader):
-                self.registered_plugins.append(plugin)
+                if plugin not in self.registered_plugins:
+                    self.registered_plugins.append(plugin)
             else:
                 raise ValueError
         except ValueError: