diff --git a/haas/plugins/discoverer.py b/haas/plugins/discoverer.py
index bb9a997..ff52ba1 100644
--- a/haas/plugins/discoverer.py
+++ b/haas/plugins/discoverer.py
@@ -41,10 +41,11 @@ def test_error(self):
 
 
 def get_relpath(top_level_directory, fullpath):
+    normalized_top_level = os.path.normpath(top_level_directory)
     normalized = os.path.normpath(fullpath)
     logger.debug('Determine if %r is within %r',
-                 normalized, top_level_directory)
-    relpath = os.path.relpath(normalized, top_level_directory)
+                 normalized, normalized_top_level)
+    relpath = os.path.relpath(normalized, normalized_top_level)
     logger.debug('Relative path is %r', relpath)
     if os.path.isabs(relpath) or relpath.startswith('..'):
         raise ValueError('Path not within project: {0}'.format(fullpath))