diff --git a/IPython/nbconvert/exporters/markdown.py b/IPython/nbconvert/exporters/markdown.py
index 28708ae..9c8abf5 100644
--- a/IPython/nbconvert/exporters/markdown.py
+++ b/IPython/nbconvert/exporters/markdown.py
@@ -26,7 +26,7 @@ class MarkdownExporter(TemplateExporter):
     """
     
     def _file_extension_default(self):
-        return 'md'
+        return '.md'
 
     def _template_file_default(self):
         return 'markdown'
diff --git a/IPython/nbconvert/exporters/notebook.py b/IPython/nbconvert/exporters/notebook.py
index 61c9bc6..20bf32a 100644
--- a/IPython/nbconvert/exporters/notebook.py
+++ b/IPython/nbconvert/exporters/notebook.py
@@ -18,7 +18,7 @@ class NotebookExporter(Exporter):
         """
     )
     def _file_extension_default(self):
-        return 'ipynb'
+        return '.ipynb'
 
     output_mimetype = 'application/json'