diff --git a/install.sh b/install.sh
index c794623..67349ad 100755
--- a/install.sh
+++ b/install.sh
@@ -7,10 +7,10 @@ nvm_has() {
 }
 
 nvm_default_install_dir() {
-  if [ -n "$XDG_CONFIG_HOME" ]; then
-    printf %s "${XDG_CONFIG_HOME/nvm}"
+  if [ -n "${XDG_CONFIG_HOME-}" ]; then
+    printf %s "${XDG_CONFIG_HOME}/nvm"
   else
-    printf %s "$HOME/.nvm"
+    printf %s "${HOME}/.nvm"
   fi
 }