diff --git a/control/HTTPResponse.php b/control/HTTPResponse.php
index daa5b763e..d52b8bc18 100755
--- a/control/HTTPResponse.php
+++ b/control/HTTPResponse.php
@@ -98,7 +98,7 @@ class SS_HTTPResponse {
 	 *  See {@link setStatusCode()} for more information.
 	 */
 	function __construct($body = null, $statusCode = null, $statusDescription = null) {
-		$this->body = $body;
+		$this->setBody($body);
 		if($statusCode) $this->setStatusCode($statusCode, $statusDescription);
 	}
 	
@@ -150,6 +150,9 @@ class SS_HTTPResponse {
 	
 	function setBody($body) {
 		$this->body = $body;
+		
+		// Set content-length in bytes. Use mbstring to avoid problems with mb_internal_encoding() and mbstring.func_overload
+		$this->headers['Content-Length'] = (function_exists('mb_strlen') ? mb_strlen($this->body,'8bit') : strlen($this->body));
 	}
 	
 	function getBody() {
diff --git a/tests/control/HTTPResponseTest.php b/tests/control/HTTPResponseTest.php
index 9524d5199..05b42cd23 100644
--- a/tests/control/HTTPResponseTest.php
+++ b/tests/control/HTTPResponseTest.php
@@ -13,4 +13,21 @@ class HTTPResponseTest extends SapphireTest {
 		);
 	}
 	
+	function testContentLengthHeader() {
+		$r = new SS_HTTPResponse('123ü');
+		$this->assertNotNull($r->getHeader('Content-Length'), 'Content-length header is added');
+		$this->assertEquals(
+			5, 
+			$r->getHeader('Content-Length'),
+			'Header matches actual content length in bytes'
+		);
+		
+		$r->setBody('1234ü');
+		$this->assertEquals(
+			6, 
+			$r->getHeader('Content-Length'),
+			'Header is updated when body is changed'
+		);
+	}
+	
 }
\ No newline at end of file