diff --git a/.github/rm-invalid-lowest-lock-files.php b/.github/rm-invalid-lowest-lock-files.php
new file mode 100644
index 0000000000..85d582fe62
--- /dev/null
+++ b/.github/rm-invalid-lowest-lock-files.php
@@ -0,0 +1,80 @@
+<?php
+
+array_shift($_SERVER['argv']);
+$dirs = $_SERVER['argv'];
+
+function getContentHash($composerJson)
+{
+    $relevantKeys = array(
+        'name',
+        'require',
+        'require-dev',
+        'conflict',
+        'replace',
+        'provide',
+        'minimum-stability',
+        'prefer-stable',
+        'repositories',
+        'extra',
+    );
+
+    $relevantContent = array();
+
+    foreach (array_intersect($relevantKeys, array_keys($composerJson)) as $key) {
+        $relevantContent[$key] = $composerJson[$key];
+    }
+    if (isset($composerJson['config']['platform'])) {
+        $relevantContent['config']['platform'] = $composerJson['config']['platform'];
+    }
+
+    ksort($relevantContent);
+
+    return md5(json_encode($relevantContent));
+}
+
+$composerLocks = array();
+
+foreach ($dirs as $dir) {
+    if (!file_exists($dir.'/composer.lock') || !$composerLock = @json_decode(file_get_contents($dir.'/composer.lock'), true)) {
+        echo "$dir/composer.lock not found or invalid.\n";
+        @unlink($dir.'/composer.lock');
+        continue;
+    }
+    if (!file_exists($dir.'/composer.json') || !$composerJson = @json_decode(file_get_contents($dir.'/composer.json'), true)) {
+        echo "$dir/composer.json not found or invalid.\n";
+        @unlink($dir.'/composer.lock');
+        continue;
+    }
+    if (!isset($composerLock['content-hash']) || getContentHash($composerJson) !== $composerLock['content-hash']) {
+        echo "$dir/composer.lock is outdated.\n";
+        @unlink($dir.'/composer.lock');
+        continue;
+    }
+    $composerLocks[$composerJson['name']] = array($dir, $composerLock, $composerJson);
+}
+
+foreach ($composerLocks as list($dir, $composerLock)) {
+    foreach ($composerLock['packages'] as $composerJson) {
+        if (0 !== strpos($version = $composerJson['version'], 'dev-') && '-dev' !== substr($version, -4)) {
+            continue;
+        }
+
+        if (!isset($composerLocks[$name = $composerJson['name']])) {
+            echo "$dir/composer.lock references missing $name.\n";
+            @unlink($dir.'/composer.lock');
+            continue 2;
+        }
+
+        foreach (array('minimum-stability', 'prefer-stable', 'repositories') as $key) {
+            if (array_key_exists($key, $composerLocks[$name][2])) {
+                $composerJson[$key] = $composerLocks[$name][2][$key];
+            }
+        }
+
+        if (getContentHash($composerJson) !== $composerLocks[$name][1]['content-hash']) {
+            echo "$dir/composer.lock is not in sync with $name.\n";
+            @unlink($dir.'/composer.lock');
+            continue 2;
+        }
+    }
+}
diff --git a/.travis.yml b/.travis.yml
index 882701f0db..007101fcc4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -216,7 +216,11 @@ install:
           if [[ $deps = high ]]; then
               echo "$COMPONENTS" | parallel --gnu -j10% "tfold {} 'cd {} && $COMPOSER_UP && $PHPUNIT_X$LEGACY'"
           elif [[ $deps = low ]]; then
-              echo "$COMPONENTS" | parallel --gnu -j10% "tfold {} 'cd {} && $COMPOSER_UP --prefer-lowest --prefer-stable && $PHPUNIT_X'"
+              [[ -e ~/php-ext/composer-lowest.lock.tar ]] && tar -xf ~/php-ext/composer-lowest.lock.tar
+              tar -cf ~/php-ext/composer-lowest.lock.tar --files-from /dev/null
+              php .github/rm-invalid-lowest-lock-files.php $COMPONENTS
+              echo "$COMPONENTS" | parallel --gnu -j10% "tfold {} 'cd {} && ([ -e composer.lock ] && ${COMPOSER_UP/update/install} || $COMPOSER_UP --prefer-lowest --prefer-stable) && $PHPUNIT_X'"
+              echo "$COMPONENTS" | xargs -n1 -I{} tar --append -f ~/php-ext/composer-lowest.lock.tar {}/composer.lock
           elif [[ $PHP = hhvm* ]]; then
               $PHPUNIT --exclude-group no-hhvm,benchmark,intl-data
           else