diff --git a/jaildk b/jaildk
index c260eec..d337cfb 100644
--- a/jaildk
+++ b/jaildk
@@ -133,15 +133,19 @@ jaildk_rc_rcoff() {
         # not required in run mode
         case $mode in
             start)
-                if ! test -d $j/etc/rcoff; then
-                    # in order to be backwards compatible to older jaildk
-                    # create the rcoff directory on the fly
-                    mkdir -d $j/etc/rcoff
-                    ( echo "#!/bin/sh"
-                      echo 'echo "$0 disabled in build chroot!"' ) > $j/etc/rcoff/rc
-                fi
+                if mount | egrep -q "rcoff.*build/$jail"; then
+                    bold "union mount $j/build/jail/etc already mounted"
+                else
+                    if ! test -d $j/etc/rcoff; then
+                        # in order to be backwards compatible to older jaildk
+                        # create the rcoff directory on the fly
+                        mkdir -d $j/etc/rcoff
+                        ( echo "#!/bin/sh"
+                          echo 'echo "$0 disabled in build chroot!"' ) > $j/etc/rcoff/rc
+                    fi
 
-                ex mount -t unionfs $j/etc/rcoff $j/build/$jail/etc
+                    ex mount -t unionfs $j/etc/rcoff $j/build/$jail/etc
+                fi
                 ;;
             stop)
                 # might fail if executed on a yet not union'ed etc