diff --git a/Shorewall-core/lib.common b/Shorewall-core/lib.common
index 7567123a7..205fc705f 100644
--- a/Shorewall-core/lib.common
+++ b/Shorewall-core/lib.common
@@ -766,23 +766,22 @@ mutex_on()
 		rm -f ${lockf}
 		error_message "WARNING: Stale lockfile ${lockf} removed"
 	    elif [ $lockpid -eq $$ ]; then
-                return 0
-	    elif ! ps | grep -v grep | qt grep ${lockpid}; then
+                fatal_error "Mutex_on confusion"
+	    elif ! qt ps --pid ${lockpid}; then
 		rm -f ${lockf}
 		error_message "WARNING: Stale lockfile ${lockf} from pid ${lockpid} removed"
 	    fi
 	fi
 
 	if qt mywhich lockfile; then
-	    lockfile -${MUTEX_TIMEOUT} -r1 ${lockf}
+	    lockfile -${MUTEX_TIMEOUT} -r1 ${lockf} || fatal_error "Can't lock ${lockf}"
 	    g_havemutex="rm -f ${lockf}"
 	    chmod u+w ${lockf}
 	    echo $$ > ${lockf}
 	    chmod u-w ${lockf}
 	elif qt mywhich lock; then
-	    lock ${lockf}
-	    g_havemutex="lock -u ${lockf} && rm -f ${lockf}"
-	    chmod u=r ${lockf}
+	    lock ${lockf} || fatal_error "Can't lock ${lockf}"
+	    g_havemutex="lock -u ${lockf}"
 	else
 	    while [ -f ${lockf} -a ${try} -lt ${MUTEX_TIMEOUT} ] ; do
 		sleep 1