diff --git a/src/Composer/Autoload/ClassMapGenerator.php b/src/Composer/Autoload/ClassMapGenerator.php
index cb8a548f2..c291f4eef 100644
--- a/src/Composer/Autoload/ClassMapGenerator.php
+++ b/src/Composer/Autoload/ClassMapGenerator.php
@@ -115,7 +115,7 @@ class ClassMapGenerator
         // strip heredocs/nowdocs
         $contents = preg_replace('{<<<\'?(\w+)\'?(?:\r\n|\n|\r)(?:.*?)(?:\r\n|\n|\r)\\1(?=\r\n|\n|\r|;)}s', 'null', $contents);
         // strip strings
-        $contents = preg_replace('{"[^"\\\\]*(\\\\.[^"\\\\]*)*"|\'[^\'\\\\]*(\\\\.[^\'\\\\]*)*\'}', 'null', $contents);
+        $contents = preg_replace('{"[^"\\\\]*(\\\\.[^"\\\\]*)*"|\'[^\'\\\\]*(\\\\.[^\'\\\\]*)*\'}s', 'null', $contents);
         // strip leading non-php code if needed
         if (substr($contents, 0, 2) !== '<?') {
             $contents = preg_replace('{^.+?<\?}s', '<?', $contents);