diff --git a/data/xsession/openbox-gnome-session.in b/data/xsession/openbox-gnome-session.in
index 1f17edbc..8dd799c0 100644
--- a/data/xsession/openbox-gnome-session.in
+++ b/data/xsession/openbox-gnome-session.in
@@ -37,7 +37,7 @@ else
   if test -z "$SESSION"; then
       # if its empty then just run openbox
       SESSION="[openbox]"
-  elif echo "$SESSION" | grep -q openbox; then
+  elif ! echo "$SESSION" | grep -q openbox; then
       # if openbox isn't in the session then append it
       SESSION="${SESSION%]},openbox]"
   fi