diff --git a/spyderlib/widgets/projectexplorer.py b/spyderlib/widgets/projectexplorer.py
index <HASH>..<HASH> 100644
--- a/spyderlib/widgets/projectexplorer.py
+++ b/spyderlib/widgets/projectexplorer.py
@@ -594,11 +594,14 @@ class ExplorerTreeWidget(OneColumnTree):
 

     def get_source_project(self, fname):

         """Return project which contains source *fname*"""

-        for project in self.projects:

-            if project.is_file_in_project(fname):

-                return project

-        else:

-            return self.default_project

+        return self.default_project # See Issue 490

+        # See Issue 490: always using the default project to avoid performance 

+        # issues with 'rope' when dealing with projects containing large files

+#        for project in self.projects:

+#            if project.is_file_in_project(fname):

+#                return project

+#        else:

+#            return self.default_project

         

     def get_project_from_name(self, name):

         for project in self.projects:
(Fixes Issue <I>) Editor: code completion was sometimes very slow when editing files within a Spyder project