diff --git a/system/HTTP/IncomingRequest.php b/system/HTTP/IncomingRequest.php
index d5b34d2c0b2b..a05c00710a95 100755
--- a/system/HTTP/IncomingRequest.php
+++ b/system/HTTP/IncomingRequest.php
@@ -294,7 +294,7 @@ public function isSecure(): bool
 	 */
 	public function getVar($index = null, $filter = null, $flags = null)
 	{
-		if ($this->isJSON())
+		if (strpos($this->getHeaderLine('Content-Type'), 'application/json') !== false)
 		{
 			if (is_null($index))
 			{
diff --git a/system/HTTP/Message.php b/system/HTTP/Message.php
index 93dbe3f318a0..edcf23215244 100644
--- a/system/HTTP/Message.php
+++ b/system/HTTP/Message.php
@@ -132,24 +132,4 @@ public function getProtocolVersion(): string
 	{
 		return $this->protocolVersion ?? '1.1';
 	}
-
-	/**
-	 * Determines if this is a json message based on the Content-Type header
-	 *
-	 * @return boolean
-	 *
-	 * @deprecated Use header calls directly
-	 */
-	public function isJSON()
-	{
-		if (! $this->hasHeader('Content-Type'))
-		{
-			return false;
-		}
-
-		$header = $this->header('Content-Type')->getValue();
-		$parts  = explode(';', $header);
-
-		return in_array('application/json', $parts, true);
-	}
 }
diff --git a/system/Validation/Validation.php b/system/Validation/Validation.php
index ea3a00958e32..1d52edc9f558 100644
--- a/system/Validation/Validation.php
+++ b/system/Validation/Validation.php
@@ -346,7 +346,7 @@ protected function processRules(string $field, string $label = null, $value, $ru
 	 */
 	public function withRequest(RequestInterface $request): ValidationInterface
 	{
-		if ($request->isJSON())
+		if (strpos($request->getHeaderLine('Content-Type'), 'application/json') !== false)
 		{
 			$this->data = $request->getJSON(true);
 			return $this;
diff --git a/tests/system/HTTP/MessageTest.php b/tests/system/HTTP/MessageTest.php
index 3972a63fdd33..f94826d41701 100644
--- a/tests/system/HTTP/MessageTest.php
+++ b/tests/system/HTTP/MessageTest.php
@@ -331,28 +331,4 @@ public function testPopulateHeaders()
 		$this->message->removeHeader('accept-language');
 		$_SERVER = $original; // restore so code coverage doesn't break
 	}
-
-	public function testIsJsonReturnsFalseWithNoHeader()
-	{
-		$this->assertFalse($this->message->isJSON());
-	}
-
-	public function testIsJsonReturnsFalseWithWrongContentType()
-	{
-		$this->message->setHeader('Content-Type', 'application/xml');
-		$this->assertFalse($this->message->isJSON());
-	}
-
-	public function testIsJsonReturnsTrue()
-	{
-		$this->message->setHeader('Content-Type', 'application/json');
-		$this->assertTrue($this->message->isJSON());
-	}
-
-	public function testIsJsonWorksWithExtendedContentType()
-	{
-		$this->message->setHeader('Content-Type', 'application/json;charset=UTF-8');
-		$this->assertTrue($this->message->isJSON());
-	}
-
 }