diff --git a/src/LaunchDarkly/Impl/Integrations/FileDataFeatureRequester.php b/src/LaunchDarkly/Impl/Integrations/FileDataFeatureRequester.php
index 9388b1b2..b09ff713 100644
--- a/src/LaunchDarkly/Impl/Integrations/FileDataFeatureRequester.php
+++ b/src/LaunchDarkly/Impl/Integrations/FileDataFeatureRequester.php
@@ -70,7 +70,7 @@ private function loadFile($filePath, &$flags, &$segments)
         $content = file_get_contents($filePath);
         $data = json_decode($content, true);
         if ($data == null) {
-            throw new \InvalidArgumentException("File is not valid JSON: " + $filePath);
+            throw new \InvalidArgumentException("File is not valid JSON: " . $filePath);
         }
         if (isset($data['flags'])) {
             foreach ($data['flags'] as $key => $value) {