diff --git a/.travis.yml b/.travis.yml
index 1331d7562a..ad8681c171 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -14,7 +14,6 @@ cache:
 before_install:
   - mv ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/xdebug.ini{,.disabled} || echo "xdebug not available"
   - travis_retry composer self-update
-  - travis_retry composer config --unset platform.php
 
 install:
   - rm composer.lock
diff --git a/build-phar.sh b/build-phar.sh
index 39ace5ebce..3bf9af1e98 100755
--- a/build-phar.sh
+++ b/build-phar.sh
@@ -2,4 +2,10 @@
 
 ./download-box.sh
 
+# lock PHP to minimum allowed version
+composer config platform.php 7.1.0
+composer update
+
 php box.phar compile -vv
+
+composer config --unset platform
diff --git a/composer.json b/composer.json
index d6c90f2413..c13d8033dc 100644
--- a/composer.json
+++ b/composer.json
@@ -54,8 +54,5 @@
     },
     "bin": [
         "bin/doctrine-migrations"
-    ],
-    "platform": {
-        "php": "7.1.x"
-    }
+    ]
 }