diff --git a/completions/system.completion.sh b/completions/system.completion.sh
index 24743d1b2..18200b6bb 100644
--- a/completions/system.completion.sh
+++ b/completions/system.completion.sh
@@ -1,27 +1,44 @@
 #! bash oh-my-bash.module
 
-# Loads the system's Bash completion modules.
-# If Homebrew is installed (OS X), its Bash completion modules are loaded.
+# Loads one of the system's Bash-completion modules.
 
-if [ -f /etc/bash_completion ]; then
-  . /etc/bash_completion
-fi
-
-# Some distribution makes use of a profile.d script to import completion.
-if [ -f /etc/profile.d/bash_completion.sh ]; then
-  . /etc/profile.d/bash_completion.sh
-fi
+# If bash-completion is already enabled (by e.g. /etc/bash.bashrc sourced from
+# /etc/profile or directly executed by Bash), we skip loading bash-completion.
+[[ ${BASH_COMPLETION_VERSINFO-} ]] && return 0
 
+# We skip loading bash-completion in the POSIX mode.  Older versions of
+# bash-completion do not work in the POSIX mode.
+shopt -oq posix && return 0
 
-if [ $(uname) = "Darwin" ] && _omb_util_command_exists brew; then
+# If Homebrew is installed (OS X), its Bash completion module is loaded.
+if is_os darwin && _omb_util_command_exists brew; then
   BREW_PREFIX=$(brew --prefix)
 
-  if [ -f "$BREW_PREFIX"/etc/bash_completion ]; then
-    . "$BREW_PREFIX"/etc/bash_completion
+  # homebrew/versions/bash-completion2 (required for projects.completion.bash)
+  # is installed to this path
+  if [[ -f "$BREW_PREFIX"/share/bash-completion/bash_completion ]]; then
+    source "$BREW_PREFIX"/share/bash-completion/bash_completion
+    return "$?"
   fi
 
-  # homebrew/versions/bash-completion2 (required for projects.completion.bash) is installed to this path
-  if [ -f "$BREW_PREFIX"/share/bash-completion/bash_completion ]; then
-    . "$BREW_PREFIX"/share/bash-completion/bash_completion
+  if [[ -f "$BREW_PREFIX"/etc/bash_completion ]]; then
+    source "$BREW_PREFIX"/etc/bash_completion
+    return "$?"
   fi
 fi
+
+if [[ -f /usr/share/bash-completion/bash_completion ]]; then
+  # bash-completion v2 is installed at this location
+  source /usr/share/bash-completion/bash_completion
+  return "$?"
+elif [[ -f /etc/bash_completion ]]; then
+  # bash-completion v1 is installed at this location
+  source /etc/bash_completion
+  return "$?"
+fi
+
+if [[ -f /etc/profile.d/bash_completion.sh ]]; then
+  # Some distribution makes use of a profile.d script to import completion.
+  source /etc/profile.d/bash_completion.sh
+  return "$?"
+fi
diff --git a/lib/base.sh b/lib/base.sh
index c9ed54a22..e9d6b4d93 100644
--- a/lib/base.sh
+++ b/lib/base.sh
@@ -229,9 +229,9 @@ function ii {
   echo -e "\\n${_omb_term_brown}Users logged on:$NC " ; w -h
   echo -e "\\n${_omb_term_brown}Current date :$NC " ; date
   echo -e "\\n${_omb_term_brown}Machine stats :$NC " ; uptime
-  [[ "$OSTYPE" == darwin* ]] && echo -e "\\n${_omb_term_brown}Current network location :$NC " ; scselect
+  is_os darwin && echo -e "\\n${_omb_term_brown}Current network location :$NC " ; scselect
   echo -e "\\n${_omb_term_brown}Public facing IP Address :$NC " ;myip
-  [[ "$OSTYPE" == darwin* ]] && echo -e "\\n${_omb_term_brown}DNS Configuration:$NC " ; scutil --dns
+  is_os darwin && echo -e "\\n${_omb_term_brown}DNS Configuration:$NC " ; scutil --dns
   echo
 }
 
@@ -257,7 +257,7 @@ function batch_chmod {
 #   usage: disk usage per directory, in Mac OS X and Linux
 #   -------------------------------------------------------------------
 function usage {
-  if [ "$(uname)" = "Darwin" ]; then
+  if is_os darwin; then
     if [ -n "$1" ]; then
       du -hd 1 "$1"
     else
diff --git a/lib/bourne-shell.sh b/lib/bourne-shell.sh
index 64499f125..5ec0875f8 100644
--- a/lib/bourne-shell.sh
+++ b/lib/bourne-shell.sh
@@ -98,14 +98,3 @@ fi
 if [ -f ~/.bashrc.local ]; then
     . ~/.bashrc.local
 fi
-
-# enable programmable completion features (you don't need to enable
-# this, if it's already enabled in /etc/bash.bashrc and /etc/profile
-# sources /etc/bash.bashrc).
-if ! shopt -oq posix; then
-  if [ -f /usr/share/bash-completion/bash_completion ]; then
-    . /usr/share/bash-completion/bash_completion
-  elif [ -f /etc/bash_completion ]; then
-    . /etc/bash_completion
-  fi
-fi
diff --git a/lib/functions.sh b/lib/functions.sh
index 37202690e..7e87d6695 100644
--- a/lib/functions.sh
+++ b/lib/functions.sh
@@ -31,7 +31,7 @@ function open_command() {
   esac
 
   # don't use nohup on OSX
-  if [[ "$OSTYPE" == darwin* ]]; then
+  if is_os darwin; then
     $open_cmd "$@" &>/dev/null
   else
     nohup $open_cmd "$@" &>/dev/null
diff --git a/lib/utils.sh b/lib/utils.sh
index d2e01b546..c1e83c192 100644
--- a/lib/utils.sh
+++ b/lib/utils.sh
@@ -40,7 +40,7 @@
 #   exit 1
 # fi
 
-# if is_os "darwin"; then
+# if is_os darwin; then
 #   e_success "You are on a mac"
 # else
 #   e_error "You are not on a mac"
@@ -255,7 +255,7 @@ function is_confirmed {
 #
 # Test which OS the user runs
 # $1 = OS to test
-# Usage: if is_os 'darwin'; then
+# Usage: if is_os darwin; then
 #
 function is_os {
   [[ $OSTYPE == $1* ]]
@@ -344,7 +344,7 @@ function _omb_util_add_prompt_command {
 
     # Set OS dependent exact match regular expression
     local prompt_re
-    if [[ $OSTYPE == darwin* ]]; then
+    if is_os darwin; then
       # macOS
       prompt_re='[[:<:]]'$hook'[[:>:]]'
     else
diff --git a/oh-my-bash.sh b/oh-my-bash.sh
index 689a49953..47de61579 100644
--- a/oh-my-bash.sh
+++ b/oh-my-bash.sh
@@ -117,7 +117,7 @@ _omb_module_require_lib "${_omb_init_files[@]}"
 unset -v _omb_init_files
 
 # Figure out the SHORT hostname
-if [[ $OSTYPE = darwin* ]]; then
+if is_os darwin; then
   # macOS's $HOST changes with dhcp, etc. Use ComputerName if possible.
   SHORT_HOST=$(scutil --get ComputerName 2>/dev/null) || SHORT_HOST=${HOST/.*}
 else
diff --git a/templates/bashrc.osh-template b/templates/bashrc.osh-template
index 4f1851d98..ad0d3aab3 100644
--- a/templates/bashrc.osh-template
+++ b/templates/bashrc.osh-template
@@ -84,6 +84,7 @@ OMB_USE_SUDO=true
 # Example format: completions=(ssh git bundler gem pip pip3)
 # Add wisely, as too many completions slow down shell startup.
 completions=(
+  system
   git
   composer
   ssh
diff --git a/themes/rjorgenson/rjorgenson.theme.sh b/themes/rjorgenson/rjorgenson.theme.sh
index 57c37a727..798d86f3a 100644
--- a/themes/rjorgenson/rjorgenson.theme.sh
+++ b/themes/rjorgenson/rjorgenson.theme.sh
@@ -16,7 +16,7 @@ SCM_SVN_CHAR="${_omb_prompt_bold_teal}⑆${_omb_prompt_normal}"
 SCM_HG_CHAR="${_omb_prompt_bold_brown}☿${_omb_prompt_normal}"
 
 PROMPT_CHAR="${OMB_THEME_BRACKET_COLOR}➞ ${_omb_prompt_normal}"
-if [[ $OSTYPE == *darwin* ]]; then
+if is_os darwin; then
   PROMPT_CHAR="${OMB_THEME_BRACKET_COLOR}➞  ${_omb_prompt_normal}"
 fi