diff --git a/.travis.yml b/.travis.yml
index d8046c1..758927e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,11 +9,7 @@ install:
   - pip install ruamel.yaml
 
 script:
-  - >-
-    git clone https://${GH_TOKEN}@github.com/cotes2020/blog-builder.git
-    ../blog-builder --depth=1 -q
-  - cp -r ../blog-builder/framework/* .
-  - bash _cibuild.sh
+  - bash _scripts/travis/cibuild.sh
 
 branches:
   only: master
diff --git a/_scripts/travis/cibuild.sh b/_scripts/travis/cibuild.sh
new file mode 100644
index 0000000..1d61786
--- /dev/null
+++ b/_scripts/travis/cibuild.sh
@@ -0,0 +1,28 @@
+#!/bin/bash
+
+# Travis CI build jobs.
+#
+# © 2019 Cotes Chung
+# Published under MIT License
+
+if [[ $TRAVIS_PULL_REQUEST = "false" ]]; then # triggered by author
+
+  BUILDER=../blog-builder
+
+  git clone https://${GH_TOKEN}@github.com/cotes2020/blog-builder.git \
+    $BUILDER --depth=1 -q
+
+  cp -r $BUILDER/framework/* .
+  bash _cibuild.sh
+
+else # triggered by Pull Request
+
+  bundle install --path vendor/bundle --quiet
+  python _scripts/py/init_all.py
+
+  build_cmd="JEKYLL_ENV=production bundle exec jekyll build"
+
+  echo "\$ $build_cmd"
+  eval $build_cmd
+
+fi