if test $# = 0
        then
-               case "${DISPLAY+set}${SESSIONNAME+set}${MSYSTEM+set}${SECURITYSESSIONID+set}" in
-               '')     set git log ;;
-               set*)   set gitk ;;
-               esac
+               if test -n "${DISPLAY+set}${SESSIONNAME+set}${MSYSTEM+set}${SECURITYSESSIONID+set}" &&
+                  type gitk >/dev/null 2>&1; then
+                       set gitk
+               else
+                       set git log
+               fi
        else
                case "$1" in
                git*|tig) ;;