diff --git a/install.sh b/install.sh
index 2bf513a..b391c4b 100755
--- a/install.sh
+++ b/install.sh
@@ -470,6 +470,6 @@ nvm_reset() {
     nvm_do_install nvm_reset nvm_default_install_dir nvm_grep
 }
 
-[ "_$NVM_ENV" = "_testing" ] || nvm_do_install
+[ "_${NVM_ENV-}" = "_testing" ] || nvm_do_install
 
 } # this ensures the entire script is downloaded #