diff --git a/core-modules/000QubesVm.py b/core-modules/000QubesVm.py
index ab6b180c..15b6f01c 100644
--- a/core-modules/000QubesVm.py
+++ b/core-modules/000QubesVm.py
@@ -1440,7 +1440,7 @@ class QubesVm(object):
             if os.name == 'nt':
                 # see here for the explanation (_exec doc):
                 #  http://msdn.microsoft.com/en-us/library/431x4c1w.aspx
-                args[0] = '"%"' % args[0]
+                args[0] = '"%s"' % args[0]
             os.execv(system_path["qrexec_client_path"], args)
             exit(1)