diff --git a/lib/galaxy/tools/wrappers.py b/lib/galaxy/tools/wrappers.py
index 38e1956758e..0aeb0f2afe1 100644
--- a/lib/galaxy/tools/wrappers.py
+++ b/lib/galaxy/tools/wrappers.py
@@ -300,13 +300,13 @@ class DatasetCollectionWrapper( object, HasDatasets ):
             element_instances[element_identifier] = element_wrapper
             element_instance_list.append( element_wrapper )
 
-        self.element_instances = element_instances
-        self.element_instance_list = element_instance_list
+        self.__element_instances = element_instances
+        self.__element_instance_list = element_instance_list
 
     def keys( self ):
         if not self.__input_supplied:
             return []
-        return self.element_instances.keys()
+        return self.__element_instances.keys()
 
     @property
     def is_collection( self ):
@@ -320,21 +320,21 @@ class DatasetCollectionWrapper( object, HasDatasets ):
         if not self.__input_supplied:
             return None
         if isinstance( key, int ):
-            return self.element_instance_list[ key ]
+            return self.__element_instance_list[ key ]
         else:
-            return self.element_instances[ key ]
+            return self.__element_instances[ key ]
 
     def __getattr__( self, key ):
         if not self.__input_supplied:
             return None
-        return self.element_instances[ key ]
+        return self.__element_instances[ key ]
 
     def __iter__( self ):
         if not self.__input_supplied:
             return [].__iter__()
-        return self.element_instance_list.__iter__()
+        return self.__element_instance_list.__iter__()
 
     def __nonzero__( self ):
         # Fail `#if $param` checks in cheetah is optional input
         # not specified or if resulting collection is empty.
-        return self.__input_supplied and bool( self.element_instance_list )
+        return self.__input_supplied and bool( self.__element_instance_list )