diff --git a/lib/directories.sh b/lib/directories.sh
index 8b16093..6ea5399 100644
--- a/lib/directories.sh
+++ b/lib/directories.sh
@@ -1,29 +1,31 @@
 #! bash oh-my-bash.module
 # Common directories functions
 
-# A clone of Zsh `cd` builtin command
-function cd() {
-  declare oldpwd="$OLDPWD"
-  declare -i index
-  if [[ "$#" -eq 1 && "$1" == -[1-9]* ]]; then
-    index="${1#-}"
-    if [[ "$index" -ge "${#DIRSTACK[@]}" ]]; then
+# A clone of the Zsh `cd' builtin command.  This supports the numbered option
+# `-1', `-2', etc.
+function _omb_directories_cd {
+  local oldpwd=$OLDPWD
+  local -i index
+  if [[ $# -eq 1 && $1 =~ ^-[1-9]+$ ]]; then
+    index=${1#-}
+    if ((index >= ${#DIRSTACK[@]})); then
       builtin echo "cd: no such entry in dir stack" >&2
       return 1
     fi
-    set -- "${DIRSTACK[$index]}"
+    set -- "${DIRSTACK[index]}"
   fi
   builtin pushd . >/dev/null &&
-    OLDPWD="$oldpwd" builtin cd "$@" &&
-    oldpwd="$OLDPWD" &&
+    OLDPWD=$oldpwd builtin cd "$@" &&
+    oldpwd=$OLDPWD &&
     builtin pushd . >/dev/null &&
-    for ((index="${#DIRSTACK[@]}"-1; index>=1; index--)); do
-      if [[ "${DIRSTACK[0]/#~/$HOME}" == "${DIRSTACK[$index]}" ]]; then
+    for ((index = ${#DIRSTACK[@]} - 1; index >= 1; index--)); do
+      if [[ ${DIRSTACK[0]/#~/$HOME} == "${DIRSTACK[index]}" ]]; then
         builtin popd "+$index" >/dev/null || return 1
       fi
     done
-  OLDPWD="$oldpwd"
+  OLDPWD=$oldpwd
 }
+_omb_util_alias cd='_omb_directories_cd'
 
 _omb_util_alias cd..='cd ../'                         # Go back 1 directory level (for fast typers)
 _omb_util_alias ..='cd ../'                           # Go back 1 directory level
@@ -47,7 +49,7 @@ _omb_util_alias 9='cd -9'
 _omb_util_alias md='mkdir -p'
 _omb_util_alias rd='rmdir'
 _omb_util_alias d='dirs -v | head -10'
-_omb_util_alias po=popd
+_omb_util_alias po='popd'
 
 # List directory contents
 _omb_util_alias lsa='ls -lha'