diff --git a/nvm.sh b/nvm.sh
index 8d57cae..e0eccfe 100644
--- a/nvm.sh
+++ b/nvm.sh
@@ -3078,7 +3078,7 @@ nvm() {
           nvm_ensure_default_set "${provided_version}"
         fi
 
-        if [ -n "${ALIAS}" ]; then
+        if [ -n "${ALIAS-}" ]; then
           nvm alias "${ALIAS}" "${provided_version}"
         fi