diff --git a/rotator/__init__.py b/rotator/__init__.py
index 1218ac7..68a8b76 100644
--- a/rotator/__init__.py
+++ b/rotator/__init__.py
@@ -19,7 +19,9 @@ def get_files_in_dir(path, regex, timeformat, recurse=False):
     for root,dirs,files in os.walk(path, topdown=False):
         for f in files:
             prefix, timestamp = parse_filename(f, regex, timeformat)
-            if prefix and prefix not in res:
+            if not prefix:
+                continue
+            if prefix not in res:
                 res[prefix] = set()
             res[prefix].add((os.path.join(root,f), timestamp))
         if not recurse: