diff --git a/composer.json b/composer.json
index 604357a..56eeee7 100644
--- a/composer.json
+++ b/composer.json
@@ -1,7 +1,7 @@
 {
     "name": "flagsmith/flagsmith-php-client",
     "type": "library",
-    "version": "v4.2.0",
+    "version": "v4.2.1",
     "license": "BSD-3-Clause",
     "authors": [
         {
diff --git a/src/Utils/IdentitiesGenerator.php b/src/Utils/IdentitiesGenerator.php
index 2285ec7..89eaa1c 100644
--- a/src/Utils/IdentitiesGenerator.php
+++ b/src/Utils/IdentitiesGenerator.php
@@ -23,6 +23,7 @@ public static function generateIdentitiesData(string $identifier, ?object $trait
     public static function generateIdentitiesCacheKey(string $identifier, ?object $traits)
     {
         $hashedTraits = $traits !== null ? '.'.sha1(serialize($traits)) : '';
-        return 'Identity.'.$identifier.$hashedTraits;
+        $hashedIdentifier = sha1($identifier);
+        return 'Identity.'.$hashedIdentifier.$hashedTraits;
     }
 }