diff --git a/src/Transport/Http.php b/src/Transport/Http.php
index db00f45..5ee2c0b 100644
--- a/src/Transport/Http.php
+++ b/src/Transport/Http.php
@@ -682,9 +682,15 @@ private function prepareWrite($sql, array $bindings = [], array $querySettings =
 
         $query = $this->prepareQuery($sql, $bindings);
 
-        if (strpos($sql, 'ON CLUSTER') === false) {
+        // strpos acts as a fast filter (cheap substring check)
+        // preg_match is used only for strict SQL keyword validation (word-boundary safe)
+        if (
+            strpos($sql, 'ON CLUSTER') === false
+            || !preg_match("/\\bON\\s+CLUSTER\\b/i", $sql)
+        ) {
             return $this->getRequestWrite($query, $querySettings);
         }
+
         if (
             !str_starts_with($sql, 'CREATE')
             && !str_starts_with($sql, 'DROP')
diff --git a/tests/ClientTest.php b/tests/ClientTest.php
index 58d49cc..b0a216a 100644
--- a/tests/ClientTest.php
+++ b/tests/ClientTest.php
@@ -1096,4 +1096,22 @@ public function testStreamInsertFormatJSONEachRow()
         $this->assertEquals(count(file($file_name)), $statement->count());
     }
 
+    public function testInsertWithOnClusterInData()
+    {
+        $this->client->write('DROP TABLE IF EXISTS `test`');
+        $this->client->write('CREATE TABLE `test` (
+                place String
+        ) ENGINE = TinyLog()');
+        $this->client->insert(
+            'test',
+            [
+                ['REGION CLUSTER'],
+            ],
+            ['place']
+        );
+
+        $statement = $this->client->select('SELECT place FROM `test`');
+        $this->assertCount(1, $statement->rows());
+        $this->assertEquals('REGION CLUSTER', $statement->fetchOne('place'));
+    }
 }