diff --git a/lib/private/AppFramework/Middleware/NotModifiedMiddleware.php b/lib/private/AppFramework/Middleware/NotModifiedMiddleware.php
index 17b423164f6..08b30092155 100644
--- a/lib/private/AppFramework/Middleware/NotModifiedMiddleware.php
+++ b/lib/private/AppFramework/Middleware/NotModifiedMiddleware.php
@@ -29,7 +29,7 @@ class NotModifiedMiddleware extends Middleware {
 		}
 
 		$modifiedSinceHeader = $this->request->getHeader('IF_MODIFIED_SINCE');
-		if ($modifiedSinceHeader !== '' && $response->getLastModified() !== null && trim($modifiedSinceHeader) === $response->getLastModified()->format(\DateTimeInterface::RFC2822)) {
+		if ($modifiedSinceHeader !== '' && $response->getLastModified() !== null && trim($modifiedSinceHeader) === $response->getLastModified()->format(\DateTimeInterface::RFC7231)) {
 			$response->setStatus(Http::STATUS_NOT_MODIFIED);
 			return $response;
 		}
diff --git a/lib/public/AppFramework/Http/Response.php b/lib/public/AppFramework/Http/Response.php
index 8037243d7a4..bdebb12c00d 100644
--- a/lib/public/AppFramework/Http/Response.php
+++ b/lib/public/AppFramework/Http/Response.php
@@ -96,7 +96,7 @@ class Response {
 			$time = \OCP\Server::get(ITimeFactory::class);
 			$expires->setTimestamp($time->getTime());
 			$expires->add(new \DateInterval('PT' . $cacheSeconds . 'S'));
-			$this->addHeader('Expires', $expires->format(\DateTimeInterface::RFC2822));
+			$this->addHeader('Expires', $expires->format(\DateTimeInterface::RFC7231));
 		} else {
 			$this->addHeader('Cache-Control', 'no-cache, no-store, must-revalidate');
 			unset($this->headers['Expires']);
@@ -238,7 +238,7 @@ class Response {
 		];
 
 		if ($this->lastModified) {
-			$mergeWith['Last-Modified'] = $this->lastModified->format(\DateTimeInterface::RFC2822);
+			$mergeWith['Last-Modified'] = $this->lastModified->format(\DateTimeInterface::RFC7231);
 		}
 
 		if ($this->ETag) {
diff --git a/tests/lib/AppFramework/Http/ResponseTest.php b/tests/lib/AppFramework/Http/ResponseTest.php
index 28614b14b40..c129b5637c5 100644
--- a/tests/lib/AppFramework/Http/ResponseTest.php
+++ b/tests/lib/AppFramework/Http/ResponseTest.php
@@ -229,7 +229,7 @@ class ResponseTest extends \Test\TestCase {
 
 		$headers = $this->childResponse->getHeaders();
 		$this->assertEquals('private, max-age=33, must-revalidate', $headers['Cache-Control']);
-		$this->assertEquals('Thu, 15 Jan 1970 06:56:40 +0000', $headers['Expires']);
+		$this->assertEquals('Thu, 15 Jan 1970 06:56:40 GMT', $headers['Expires']);
 	}
 
 
@@ -239,7 +239,7 @@ class ResponseTest extends \Test\TestCase {
 		$lastModified->setTimestamp(1);
 		$this->childResponse->setLastModified($lastModified);
 		$headers = $this->childResponse->getHeaders();
-		$this->assertEquals('Thu, 01 Jan 1970 00:00:01 +0000', $headers['Last-Modified']);
+		$this->assertEquals('Thu, 01 Jan 1970 00:00:01 GMT', $headers['Last-Modified']);
 	}
 
 	public function testChainability(): void {
@@ -257,7 +257,7 @@ class ResponseTest extends \Test\TestCase {
 		$this->assertEquals('world', $headers['hello']);
 		$this->assertEquals(Http::STATUS_NOT_FOUND, $this->childResponse->getStatus());
 		$this->assertEquals('hi', $this->childResponse->getEtag());
-		$this->assertEquals('Thu, 01 Jan 1970 00:00:01 +0000', $headers['Last-Modified']);
+		$this->assertEquals('Thu, 01 Jan 1970 00:00:01 GMT', $headers['Last-Modified']);
 		$this->assertEquals('private, max-age=33, must-revalidate',
 			$headers['Cache-Control']);
 	}
diff --git a/tests/lib/AppFramework/Middleware/NotModifiedMiddlewareTest.php b/tests/lib/AppFramework/Middleware/NotModifiedMiddlewareTest.php
index 204cc647cad..d80df1841c8 100644
--- a/tests/lib/AppFramework/Middleware/NotModifiedMiddlewareTest.php
+++ b/tests/lib/AppFramework/Middleware/NotModifiedMiddlewareTest.php
@@ -43,13 +43,13 @@ class NotModifiedMiddlewareTest extends \Test\TestCase {
 			[null, '"etag"', null, '', false],
 			['etag', '"etag"', null, '', true],
 
-			[null, '', $now, $now->format(\DateTimeInterface::RFC2822), true],
+			[null, '', $now, $now->format(\DateTimeInterface::RFC7231), true],
 			[null, '', $now, $now->format(\DateTimeInterface::ATOM), false],
-			[null, '', null, $now->format(\DateTimeInterface::RFC2822), false],
+			[null, '', null, $now->format(\DateTimeInterface::RFC7231), false],
 			[null, '', $now, '', false],
 
 			['etag', '"etag"', $now, $now->format(\DateTimeInterface::ATOM), true],
-			['etag', '"etag"', $now, $now->format(\DateTimeInterface::RFC2822), true],
+			['etag', '"etag"', $now, $now->format(\DateTimeInterface::RFC7231), true],
 		];
 	}