diff --git a/contrib/onelab/python/onelab.py b/contrib/onelab/python/onelab.py
index 6f16aea0f5056f06651f4a0ac41e35b935df31b9..01195a7af8c9dbfee085487af3b0f40e87cd6923 100755
--- a/contrib/onelab/python/onelab.py
+++ b/contrib/onelab/python/onelab.py
@@ -34,7 +34,8 @@ def path(dirname, inp):
   # dirname is a directory, can be empty
   # inp is an optional file or subdirectory name
   # returns the path to 'inp' in the same directory as 'ref' 
-  dirname = os.path.dirname(dirname + os.sep)
+  if dirname:
+    dirname = os.path.dirname(dirname + os.sep)
   if not inp: 
     return dirname
   if inp[0] == '/' or inp[0] == '\\' or (len(inp) > 2 and inp[1] == '\:'):