diff --git a/tools/check_for_upgrade.sh b/tools/check_for_upgrade.sh
index 881bc6c49..223812121 100644
--- a/tools/check_for_upgrade.sh
+++ b/tools/check_for_upgrade.sh
@@ -29,6 +29,10 @@ fi
 # Cancel upgrade if git is unavailable on the system
 whence git >/dev/null || return 0
 
+# Cancel upgrade if the current user doesn't have write permissions for the
+# oh-my-zsh directory.
+[[ -w "$ZSH" ]] || return 0
+
 if [ -f ~/.zsh-update ]
 then
   . ~/.zsh-update