diff --git a/src/Composer/Autoload/ClassMapGenerator.php b/src/Composer/Autoload/ClassMapGenerator.php
index 3f1243ade..59542a4a7 100644
--- a/src/Composer/Autoload/ClassMapGenerator.php
+++ b/src/Composer/Autoload/ClassMapGenerator.php
@@ -122,18 +122,25 @@ class ClassMapGenerator
             $extraTypes .= '|enum';
         }
 
-        try {
-            $contents = Silencer::call('php_strip_whitespace', $path);
-            if (!$contents) {
-                if (!file_exists($path)) {
-                    throw new \Exception('File does not exist');
-                }
-                if (!is_readable($path)) {
-                    throw new \Exception('File is not readable');
-                }
+        // Use @ here instead of Silencer to actively suppress 'unhelpful' output
+        // @link https://github.com/composer/composer/pull/4886
+        $contents = @php_strip_whitespace($path);
+        if (!$contents) {
+            if (!file_exists($path)) {
+                $message = 'File at "%s" does not exist, check your classmap definitions';
+            } elseif (!is_readable($path)) {
+                $message = 'File at "%s" is not readable, check its permissions';
+            } elseif ('' === trim(file_get_contents($path))) {
+                // The input file was really empty and thus contains no classes
+                return array();
+            } else {
+                $message = 'File at "%s" could not be parsed as PHP, it may be binary or corrupted';
+            }
+            $error = error_get_last();
+            if (isset($error['message'])) {
+                $message .= PHP_EOL . 'The following message may be helpful:' . PHP_EOL . $error['message'];
             }
-        } catch (\Exception $e) {
-            throw new \RuntimeException('Could not scan for classes inside '.$path.": \n".$e->getMessage(), 0, $e);
+            throw new \RuntimeException(sprintf($message, $path));
         }
 
         // return early if there is no chance of matching anything in this file
diff --git a/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php b/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
index cd3d43260..13cf7cd83 100644
--- a/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
+++ b/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
@@ -113,7 +113,7 @@ class ClassMapGeneratorTest extends TestCase
 
     /**
      * @expectedException \RuntimeException
-     * @expectedExceptionMessage Could not scan for classes inside
+     * @expectedExceptionMessage does not exist
      */
     public function testFindClassesThrowsWhenFileDoesNotExist()
     {