diff --git a/tools/install.sh b/tools/install.sh
index 1a0a8e6db..ad47df785 100755
--- a/tools/install.sh
+++ b/tools/install.sh
@@ -24,7 +24,7 @@ main() {
   # which may fail on systems lacking tput or terminfo
   set -e
 
-  if command -v zsh >/dev/null 2>&1; then
+  if ! command -v zsh >/dev/null 2>&1; then
     printf "${YELLOW}Zsh is not installed!${NORMAL} Please install zsh first!\n"
     exit
   fi