diff --git a/src/AbstractWebApplication.php b/src/AbstractWebApplication.php
index ddce5a39..88556209 100644
--- a/src/AbstractWebApplication.php
+++ b/src/AbstractWebApplication.php
@@ -571,6 +571,11 @@ public function setHeader($name, $value, $replace = false)
 			$response = $response->withoutHeader($name);
 		}
 
+		if (!$replace && $response->hasHeader($name))
+		{
+			return $this;
+		}
+
 		// Add the header to the internal array.
 		$this->setResponse($response->withAddedHeader($name, $value));