diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2ae5e79..360d004 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,11 @@
 
 All notable changes to `phpkiteconnect` will be documented in this file.
 
+## 5.1.0 - 2026-03-27
+- Added `MARKET_PROTECTION_AUTO` constant (`-1`) for system-default market protection
+- Added `market_protection` parameter support for `placeOrder` and `modifyOrder`
+- Added tests for `placeOrder` and `modifyOrder` with `market_protection`
+
 ## 4.0.0 - 2021-04-06
 - Major refactor to project structure and code
 - PHP support 7.3+
diff --git a/src/KiteConnect.php b/src/KiteConnect.php
index 3263055..c2adf15 100644
--- a/src/KiteConnect.php
+++ b/src/KiteConnect.php
@@ -121,7 +121,10 @@ class KiteConnect
     public const POSITION_TYPE_DAY = "day";
     public const POSITION_TYPE_OVERNIGHT = "overnight";
 
-    public const VERSION = "3.2.0";
+    // Market protection
+    public const MARKET_PROTECTION_AUTO = -1;
+
+    public const VERSION = "5.1.0";
 
     // Kite connect header version
     private $kiteVersion = "3";
@@ -465,6 +468,7 @@ public function getMargins(?string $segment = null): mixed
      *                $params int|null "auction_number" A unique identifier for a particular auction
      *                $params float|null  "tag" (Optional) Order tag
      *                $params string|null "validity" (Optional) Order validity (DAY, IOC).
+     *                $params float    "market_protection" (Mandatory only for MARKET orders) Set to -1 for system-default market protection, or a percentage value greater than 0 up to 100
      * @return mixed|null
      * @throws DataException
      * @throws GeneralException
@@ -494,6 +498,7 @@ public function placeOrder(string $variety, array $params)
      *                $params float|null  "price" (Optional) Order Price
      *                $params float|null  "trigger_price" (Optional) Trigger price
      *                $params string|null "validity" (Optional) Order validity (DAY, IOC).
+     *                $params float|null    "market_protection" (Optional) Set to -1 for system-default market protection, or a percentage value greater than 0 up to 100
      *
      * @return mixed
      * @throws DataException
diff --git a/tests/KiteConnectTest.php b/tests/KiteConnectTest.php
index ecaafe0..949e246 100644
--- a/tests/KiteConnectTest.php
+++ b/tests/KiteConnectTest.php
@@ -204,6 +204,39 @@ public function placeOrderTest($kiteConnect): void
 
     }
 
+    /** 
+     * @depends initializeMock
+     * @test placeOrder with market_protection
+    */
+    public function placeOrderWithMarketProtectionTest($kiteConnect): void
+    {
+        $response = $kiteConnect->placeOrder("regular", [
+            "tradingsymbol" => "INFY",
+            "exchange" => "NSE",
+            "quantity" => 1,
+            "transaction_type" => "BUY",
+            "order_type" => "MARKET",
+            "product" => "NRML",
+            "market_protection" => KiteConnect::MARKET_PROTECTION_AUTO
+        ]);
+
+        $this->assertObjectHasProperty('order_id', $response);
+    }
+
+    /** 
+     * @depends initializeMock
+     * @test modifyOrder with market_protection
+    */
+    public function modifyOrderWithMarketProtectionTest($kiteConnect): void
+    {
+        $response = $kiteConnect->modifyOrder("regular", "123456789", [
+            "price" => 10,
+            "market_protection" => KiteConnect::MARKET_PROTECTION_AUTO
+        ]);
+
+        $this->assertObjectHasProperty('order_id', $response);
+    }
+
     /** 
      * @depends initializeMock
      * @test getOrders 
diff --git a/tests/MockJson.php b/tests/MockJson.php
index 4763cb3..1e277be 100644
--- a/tests/MockJson.php
+++ b/tests/MockJson.php
@@ -26,6 +26,8 @@ public function generateMock()
         $response_array[] = new Response($status_code, $header_content, $this->fetchMock("holdings.json"));
         $response_array[] = new Response($status_code, $header_content, $this->fetchMock("positions.json"));
         $response_array[] = new Response($status_code, $header_content, $this->fetchMock("order_response.json"));
+        $response_array[] = new Response($status_code, $header_content, $this->fetchMock("order_response.json"));
+        $response_array[] = new Response($status_code, $header_content, $this->fetchMock("order_modify.json"));
         $response_array[] = new Response($status_code, $header_content, $this->fetchMock("orders.json"));
         $response_array[] = new Response($status_code, $header_content, $this->fetchMock("order_info.json"));
         $response_array[] = new Response($status_code, $header_content, $this->fetchMock("order_trades.json"));