diff --git a/bin/compton-trans b/bin/compton-trans
index 91714f9..7b2ac7d 100755
--- a/bin/compton-trans
+++ b/bin/compton-trans
@@ -38,6 +38,11 @@ wid=
 topmost=
 lineno=
 
+# Workaround: replace '-5' with '~5' so as not to confuse getopts.
+for v in "$@"; do
+  shift && set -- "$@" "$(echo "$v" | sed 's/^-\([0-9]\+%\?\)$/~\1/')"
+done
+
 # This takes into account the fact that getopts stops on
 # any argument it doesn't recongize or errors on. This
 # allows for things like `compton-trans -5` as well
@@ -45,10 +50,9 @@ lineno=
 while test $# -gt 0; do
   # Reset option index
   OPTIND=1
-  LASTIND=1
 
   # Read options
-  while getopts ':scdgn:w:o:' option "$@"; do
+  while getopts 'scdgn:w:o:' option "$@"; do
     case "$option" in
       s) wprefix=''; window='' ;;
       c)
@@ -61,16 +65,8 @@ while test $# -gt 0; do
       n) wprefix='-name'; window=$OPTARG ;;
       w) wprefix='-id'; window=$OPTARG ;;
       o) opacity=$OPTARG ;;
-      \?)
-        # For some reason single char options `-x` stop on the OPTIND after the
-        # argument index, whereas two or more character options (`-foo`) stop
-        # on the argument's index, so we use LASTIND here instead. If OPTIND is
-        # not equal to LASTIND, this means -x was used instead of -xx.
-        OPTIND=$LASTIND
-        break
-      ;;
+      \?) exit 1 ;;
     esac
-    LASTIND=$OPTIND
   done
 
   # Read positional arguments
@@ -79,7 +75,7 @@ while test $# -gt 0; do
 done
 
 # clean up opacity. xargs == a poor man's trim.
-opacity=$(echo "$opacity" | sed 's/%//g' | xargs)
+opacity=$(echo "$opacity" | xargs | sed 's/%//g' | sed 's/^~\([0-9]\+\)$/-\1/')
 
 # Validate opacity value
 if test -z "$action" && ! echo "$opacity" | grep -q '^[+-]\?[0-9]\+$'; then