diff --git a/bin/settrans b/bin/settrans
index 5c4984d..609d178 100755
--- a/bin/settrans
+++ b/bin/settrans
@@ -1,21 +1,21 @@
 #!/bin/bash
 
 # transset in a bash script
-# copyright (c) 2011-2012, christopher jeffrey
+# Copyright (c) 2011-2012, Christopher Jeffrey
 
-# usage:
+# Usage:
 # by window id
-#trans -w "$WINDOWID" -o 75
+#   settrans -w "$WINDOWID" -o 75
 # by name
-#trans -n "urxvt" -o 75
+#   settrans -n "urxvt" -o 75
 # by current window
-#trans -c -o 75
+#   settrans -c -o 75
 # by selection
-#trans -s -o 75
+#   settrans -s -o 75
 # increment current window 5%
-#trans -c -o +5
+#   settrans -c -o +5
 
-if [ -z "$(which xprop)" -o -z "$(which xwininfo)" ]; then
+if test -z "$(which xprop)" -o -z "$(which xwininfo)"; then
   echo "Please install x11-utils/xorg-xprop/xorg-xwininfo." >&2
   exit 1
 fi
@@ -46,34 +46,45 @@ root=$(xwininfo -all -root \
   | sed 's/^.*\(0x\S*\).*$/\1/')
 
 parent=$window
-while [ true ]; do
+i=0
+while true; do
   parent=$(xwininfo -all $parent \
     | grep Parent \
     | sed 's/^.*\(0x\S*\).*$/\1/')
+
   if [ "$parent" = "$root" ]; then
     break
   fi
+
   parent="-id $parent"
   window=$parent
+
+  i=$((i+1))
+  if test $i -ge 1000; then
+    echo "An error occurred while traversing up the window tree." >&2
+    echo "Please report this to https://github.com/chjj/compton/issues." >&2
+    echo "Please mention your WM and versions of xwininfo/xprop." >&2
+    exit 1
+  fi
 done
 
 inc=$(echo "$opacity" | sed 's/^\(+\|-\).*$\|^.*$/\1/')
-if [ -n "$inc" ]; then
+if test -n "$inc"; then
   cur=$(xprop $window -notype "_NET_WM_WINDOW_OPACITY" \
     | sed 's/^.*\b\([0-9]\+\).*$\|^.*$/\1/')
-  [ -z "$cur" ] && cur=$((0xffffffff))
+  test -z "$cur" && cur=$((0xffffffff))
   cur=$((cur*100/0xffffffff))
   opacity=$(echo "$opacity" | sed 's/\(\+\|\-\)//')
-  if [ "$inc" = "+" ]; then
+  if test "$inc" = "+"; then
     opacity=$((cur+opacity))
   else
     opacity=$((cur-opacity))
   fi
 fi
 
-if [ -n "$opacity" ] && [ -n "$window" ]; then
-  [ $opacity -le 0 ] && opacity=0
-  [ $opacity -ge 100 ] && opacity=100
+if test -n "$opacity" -a -n "$window"; then
+  test $opacity -lt 0 && opacity=0
+  test $opacity -gt 100 && opacity=100
   opacity=$((opacity*0xffffffff/100))
   xprop $window -f _NET_WM_WINDOW_OPACITY 32c \
     -set _NET_WM_WINDOW_OPACITY "$opacity"