diff --git a/README.md b/README.md
index 58756d7..5544fe2 100644
--- a/README.md
+++ b/README.md
@@ -4,5 +4,6 @@ This [rbenv](http://rbenv.org/) plugin adds the `rbenv update` command that upda
 
 Simply clone the repository into the plugins directory:
 
-    mkdir -p $RBENV_ROOT/plugins
-    git clone https://github.com/rkh/rbenv-update.git $RBENV_ROOT/plugins/rbenv-update
+    [ -z "$RBENV_ROOT" ] && export RBENV_ROOT="$HOME/.rbenv"
+    mkdir -p "$RBENV_ROOT/plugins"
+    git clone https://github.com/rkh/rbenv-update.git "$RBENV_ROOT/plugins/rbenv-update"