diff --git a/lib/spack/spack/relocate.py b/lib/spack/spack/relocate.py
index fb4ff18fae48ab3f9e27c6c3ce86f8604944d1f9..a6aea329e15a1b7d74a7e39c8f5638c1f7a37e1b 100644
--- a/lib/spack/spack/relocate.py
+++ b/lib/spack/spack/relocate.py
@@ -412,7 +412,8 @@ def replace(match):
         if padding < 0:
             return data
         return match.group().replace(old_dir.encode('utf-8'),
-                                     new_dir.encode('utf-8')) + b'\0' * padding
+                                     os.sep.encode('utf-8') * padding +
+                                     new_dir.encode('utf-8'))
 
     with open(path_name, 'rb+') as f:
         data = f.read()