diff --git a/README.md b/README.md
index 257cb83..f7d274b 100644
--- a/README.md
+++ b/README.md
@@ -135,7 +135,7 @@ function install_powerline_precmd() {
   precmd_functions+=(powerline_precmd)
 }
 
-if [ "$TERM" != "linux" ]; then
+if [ "$TERM" != "linux" -a -x "$(command -v powerline-shell)" ]; then
     install_powerline_precmd
 fi
 ```