diff --git a/bam/__init__.py b/bam/__init__.py
index ecaf7f1..7b354c5 100644
--- a/bam/__init__.py
+++ b/bam/__init__.py
@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 
 import sys
-__version__ = "0.0.5.1"
+__version__ = "0.0.5.2"
 
 def main(argv=sys.argv):
     from .cli import main
diff --git a/bam/utils/system.py b/bam/utils/system.py
index 2c2260d..808abfe 100644
--- a/bam/utils/system.py
+++ b/bam/utils/system.py
@@ -130,20 +130,12 @@ def is_subdir(path, directory):
     Returns true if *path* in a subdirectory of *directory*.
     """
     import os
-    from os.path import normpath, normcase
+    from os.path import normpath, normcase, sep
     path = normpath(normcase(path))
     directory = normpath(normcase(directory))
-
-    if isinstance(directory, bytes):
-        sep_i = ord(os.sep)
-        sep = os.sep.encode('ascii')
-    else:
-        sep_i = os.sep
-        sep = os.sep
-
-    directory = directory.rstrip(sep)
     if len(path) > len(directory):
-        if path.startswith(directory):
-            return (path[len(directory)] == sep_i)
+        sep = sep.encode('ascii') if isinstance(directory, bytes) else sep
+        if path.startswith(directory.rstrip(sep) + sep):
+            return True
     return False