diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0214e0a..c357df9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 - WooCommerce events
 - PHP version and OPcache status information
+- error message on incomplete install
 
 ### Fixed
 - headers error from new line in Server Timing
diff --git a/laps.php b/laps.php
index 3c4ea9f..e40da4f 100644
--- a/laps.php
+++ b/laps.php
@@ -16,6 +16,10 @@ if ( file_exists( __DIR__ . '/vendor/autoload.php' ) ) {
 	require __DIR__ . '/vendor/autoload.php';
 }
 
+if ( ! class_exists( '\Rarst\Laps\Plugin' ) ) {
+	trigger_error( 'Laps not fully installed! Please install with Composer or download full release archive.', E_USER_ERROR );
+}
+
 $laps = new \Rarst\Laps\Plugin();
 
 $laps->run();