diff --git a/.travis.yml b/.travis.yml
index fd14373..7fdc791 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -21,11 +21,14 @@ matrix:
 notifications:
   irc: "chat.freenode.net#picocms"
 
+before_install:
+  - export PATH="$TRAVIS_BUILD_DIR/_build:$PATH"
+
 install:
-  - composer install
+  - install.sh
 
 before_script:
-  - export PATH="$TRAVIS_BUILD_DIR/_build:$TRAVIS_BUILD_DIR/vendor/bin:$PATH"
+  - export PATH="$TRAVIS_BUILD_DIR/vendor/bin:$PATH"
 
 script:
   - phpcs --standard=.phpcs.xml "$TRAVIS_BUILD_DIR"
diff --git a/_build/install.sh b/_build/install.sh
new file mode 100755
index 0000000..b40f7e8
--- /dev/null
+++ b/_build/install.sh
@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+
+set -e
+
+# set COMPOSER_ROOT_VERSION when necessary
+if [ -z "$TRAVIS_TAG" ] && [ "$TRAVIS_PULL_REQUEST" == "false" ]; then
+    PICO_VERSION_PATTERN="$(php -r "
+        \$json = json_decode(file_get_contents('$TRAVIS_BUILD_DIR/composer.json'), true);
+        if (\$json !== null) {
+            if (isset(\$json['extra']['branch-alias']['dev-$TRAVIS_BRANCH'])) {
+                echo 'dev-$TRAVIS_BRANCH';
+            }
+        }
+    ")"
+
+    if [ -z "$PICO_VERSION_PATTERN" ]; then
+        PICO_VERSION_PATTERN="$(php -r "
+            require_once('$TRAVIS_BUILD_DIR/lib/Pico.php');
+            echo preg_replace('/\.[0-9]+-dev$/', '.x-dev', Pico::VERSION);
+        ")"
+    fi
+
+    if [ -z "$COMPOSER_ROOT_VERSION" ] && [ -n "$PICO_VERSION_PATTERN" ]; then
+        export COMPOSER_ROOT_VERSION="$PICO_VERSION_PATTERN"
+    fi
+fi
+
+# install dependencies
+echo "Running \`composer install\`$([ -n "$COMPOSER_ROOT_VERSION" ] && echo -n " ($COMPOSER_ROOT_VERSION)")..."
+composer install