diff --git a/.travis.yml b/.travis.yml
index d07ba1f..effbd86 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -32,7 +32,7 @@ before_install:
   - zsh  --version
   - dpkg -s dash | grep ^Version | awk '{print $2}'
   # install python
-  - pyenv install 2.7.18
+  - pyenv local 2.7.18 || pyenv install 2.7.18
   - pyenv local 2.7.18 || echo 'pyenv failed'
   - python -V
 install:
diff --git a/nvm.sh b/nvm.sh
index 849dcfc..3ccb7d8 100644
--- a/nvm.sh
+++ b/nvm.sh
@@ -141,8 +141,8 @@ nvm_download() {
                             -e 's/-o /-O /' \
                             -e 's/-C - /-c /')
 
-    if [ -n "$NVM_AUTH_HEADER" ]; then
-      ARGS="$ARGS --header \"$NVM_AUTH_HEADER\""
+    if [ -n "${NVM_AUTH_HEADER:-}" ]; then
+      ARGS="${ARGS} --header \"${NVM_AUTH_HEADER}\""
     fi
     # shellcheck disable=SC2086
     eval wget $ARGS