diff --git a/lib/Controller/BoardApiController.php b/lib/Controller/BoardApiController.php
index 647072353..d7afc6dcc 100644
--- a/lib/Controller/BoardApiController.php
+++ b/lib/Controller/BoardApiController.php
@@ -85,7 +85,9 @@ class BoardApiController extends ApiController {
 	 */
 	public function get() {
 		$board = $this->boardService->find($this->request->getParam('boardId'));
-		return new DataResponse($board, HTTP::STATUS_OK);
+		$response = new DataResponse($board, HTTP::STATUS_OK);
+		$response->setETag($board->getEtag());
+		return $response;
 	}
 
 	/**
diff --git a/lib/Controller/CardApiController.php b/lib/Controller/CardApiController.php
index c9f47fb93..04d0fe4c9 100644
--- a/lib/Controller/CardApiController.php
+++ b/lib/Controller/CardApiController.php
@@ -64,7 +64,9 @@ class CardApiController extends ApiController {
 	 */
 	public function get() {
 		$card = $this->cardService->find($this->request->getParam('cardId'));
-		return new DataResponse($card, HTTP::STATUS_OK);
+		$response = new DataResponse($card, HTTP::STATUS_OK);
+		$response->setETag($card->getEtag());
+		return $response;
 	}
 
 	/**
diff --git a/lib/Controller/StackApiController.php b/lib/Controller/StackApiController.php
index 61d4c6afe..d39bd7f5b 100644
--- a/lib/Controller/StackApiController.php
+++ b/lib/Controller/StackApiController.php
@@ -83,7 +83,9 @@ class StackApiController extends ApiController {
 	 */
 	public function get() {
 		$stack = $this->stackService->find($this->request->getParam('stackId'));
-		return new DataResponse($stack, HTTP::STATUS_OK);
+		$response = new DataResponse($stack, HTTP::STATUS_OK);
+		$response->setETag($stack->getETag());
+		return $response;
 	}
 
 	/**
diff --git a/lib/Db/Board.php b/lib/Db/Board.php
index eb5ec1d07..31caa5b27 100644
--- a/lib/Db/Board.php
+++ b/lib/Db/Board.php
@@ -81,4 +81,8 @@ class Board extends RelationalEntity {
 			$this->acl[] = $a;
 		}
 	}
+
+	public function getETag() {
+		return md5((string)$this->getLastModified());
+	}
 }
diff --git a/lib/Db/Card.php b/lib/Db/Card.php
index 4e24719ba..fe91387ae 100644
--- a/lib/Db/Card.php
+++ b/lib/Db/Card.php
@@ -155,4 +155,8 @@ class Card extends RelationalEntity {
 	public function getCalendarPrefix(): string {
 		return 'card';
 	}
+
+	public function getETag() {
+		return md5((string)$this->getLastModified());
+	}
 }
diff --git a/lib/Db/Stack.php b/lib/Db/Stack.php
index 9790e6b7c..c414f52a8 100644
--- a/lib/Db/Stack.php
+++ b/lib/Db/Stack.php
@@ -65,4 +65,8 @@ class Stack extends RelationalEntity {
 	public function getCalendarPrefix(): string {
 		return 'stack';
 	}
+
+	public function getETag() {
+		return md5((string)$this->getLastModified());
+	}
 }