diff --git a/oh-my-zsh.sh b/oh-my-zsh.sh
index aeeaa3daf..732a403b7 100644
--- a/oh-my-zsh.sh
+++ b/oh-my-zsh.sh
@@ -19,13 +19,19 @@ if [[ -z "$ZSH_CUSTOM" ]]; then
     ZSH_CUSTOM="$ZSH/custom"
 fi
 
+
+is_plugin() {
+  local base_dir=$1
+  local name=$2
+  test -f $base_dir/plugins/$name/$name.plugin.zsh \
+    || test -f $base_dir/plugins/$name/_$name
+}
 # Add all defined plugins to fpath. This must be done
 # before running compinit.
-plugin=${plugin:=()}
 for plugin ($plugins); do
-  if [ -f $ZSH_CUSTOM/plugins/$plugin/$plugin.plugin.zsh ]; then
+  if is_plugin $ZSH_CUSTOM $plugin; then
     fpath=($ZSH_CUSTOM/plugins/$plugin $fpath)
-  elif [ -f $ZSH/plugins/$plugin/$plugin.plugin.zsh ]; then
+  elif is_plugin $ZSH $plugin; then
     fpath=($ZSH/plugins/$plugin $fpath)
   fi
 done