diff --git a/bin/rector_bootstrap.php b/bin/rector_bootstrap.php
index 190c9f66c7c..379b93b1c5e 100644
--- a/bin/rector_bootstrap.php
+++ b/bin/rector_bootstrap.php
@@ -12,7 +12,11 @@ $possibleAutoloadPaths = [
 foreach ($possibleAutoloadPaths as $possibleAutoloadPath) {
     if (is_file($possibleAutoloadPath)) {
         require_once $possibleAutoloadPath;
-
-        break;
+        return;
     }
 }
+
+throw new RuntimeException(sprintf(
+    'Composer autoload.php was not found in paths "%s". Have you run  "composer update"?',
+    implode('", "', $possibleAutoloadPaths)
+));