diff --git a/install.sh b/install.sh
index 7352879..82005bb 100755
--- a/install.sh
+++ b/install.sh
@@ -5,9 +5,11 @@ set errexit
 
 function prerequisites {
   if which zsh > /dev/null ; then
-    if [[ `getent passwd $USER | cut -d: -f7` != */zsh ]] ; then
-      echo 'Enter password to change shell.' >&2
-      chsh -s `which zsh`
+    if [[ $- == *i* ]] ; then
+      if [[ `getent passwd $USER | cut -d: -f7` != */zsh ]] ; then
+        echo 'Enter password to change shell.' >&2
+        chsh -s `which zsh`
+      fi
     fi
     install_git https://github.com/robbyrussell/oh-my-zsh.git $HOME/.oh-my-zsh
   else