diff --git a/src/lint/linter/ArcanistComposerLinter.php b/src/lint/linter/ArcanistComposerLinter.php
--- a/src/lint/linter/ArcanistComposerLinter.php
+++ b/src/lint/linter/ArcanistComposerLinter.php
@@ -37,11 +37,12 @@
   }
 
   private function lintComposerJson($path) {
-    $composer_hash = md5(Filesystem::readFile(dirname($path).'/composer.json'));
+    $composer_hash = self::getContentHash(
+      Filesystem::readFile(dirname($path).'/composer.json'));
     $composer_lock = phutil_json_decode(
       Filesystem::readFile(dirname($path).'/composer.lock'));
 
-    if ($composer_hash !== $composer_lock['hash']) {
+    if ($composer_hash !== $composer_lock['content-hash']) {
       $this->raiseLintAtPath(
         self::LINT_OUT_OF_DATE,
         pht(
@@ -52,4 +53,68 @@
     }
   }
 
+  /**
+   * Returns the md5 hash of the sorted content of the composer.json file.
+   *
+   * This function copied from
+   * https://github.com/
+   * composer/composer/blob/1.5.2/src/Composer/Package/Locker.php
+   * and has the following license:
+   *
+   * Copyright (c) Nils Adermann, Jordi Boggiano
+   *
+   * Permission is hereby granted, free of charge, to any person obtaining a
+   * copy of this software and associated documentation files (the "Software"),
+   * to deal in the Software without restriction, including without limitation
+   * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+   * and/or sell copies of the Software, and to permit persons to whom the
+   * Software is furnished to do so, subject to the following conditions:
+   *
+   * The above copyright notice and this permission notice shall be included in
+   * all copies or substantial portions of the Software.
+   *
+   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+   * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+   * DEALINGS IN THE SOFTWARE.
+   *
+   *
+   * @param string $composerFileContents The contents of the composer file.
+   *
+   * @return string
+   */
+  public static function getContentHash($composerFileContents) {
+    $content = json_decode($composerFileContents, true);
+
+    $relevantKeys = array(
+      'name',
+      'version',
+      'require',
+      'require-dev',
+      'conflict',
+      'replace',
+      'provide',
+      'minimum-stability',
+      'prefer-stable',
+      'repositories',
+      'extra',
+    );
+
+    $relevantContent = array();
+
+    foreach (array_intersect($relevantKeys, array_keys($content)) as $key) {
+      $relevantContent[$key] = $content[$key];
+    }
+    if (isset($content['config']['platform'])) {
+      $relevantContent['config']['platform'] = $content['config']['platform'];
+    }
+
+    ksort($relevantContent);
+
+    return md5(json_encode($relevantContent));
+  }
+
 }