diff --git a/security/Security.php b/security/Security.php
index 840af3f9d..c6c6cd402 100644
--- a/security/Security.php
+++ b/security/Security.php
@@ -336,7 +336,9 @@ class Security extends Controller implements TemplateGlobalProvider {
 		$this->getResponse()->addHeader('X-Frame-Options', $this->config()->frame_options);
 
 		// Prevent search engines from indexing the login page
-		$this->getResponse()->addHeader('X-Robots-Tag', $this->config()->robots_tag);
+		if ($this->config()->robots_tag) {
+			$this->getResponse()->addHeader('X-Robots-Tag', $this->config()->robots_tag);
+		}
 	}
 
 	public function index() {
diff --git a/tests/security/SecurityTest.php b/tests/security/SecurityTest.php
index bd2c8ed0f..a2206e37d 100644
--- a/tests/security/SecurityTest.php
+++ b/tests/security/SecurityTest.php
@@ -581,6 +581,13 @@ class SecurityTest extends FunctionalTest {
 		$this->assertContains('noindex', $robotsHeader);
 	}
 
+	public function testDoNotSendEmptyRobotsHeaderIfNotDefined() {
+		Config::inst()->update('Security', 'robots_tag', null);
+		$response = $this->get(Config::inst()->get('Security', 'login_url'));
+		$robotsHeader = $response->getHeader('X-Robots-Tag');
+		$this->assertNull($robotsHeader);
+	}
+
 	/**
 	 * Execute a log-in form using Director::test().
 	 * Helper method for the tests above