diff --git a/apps/dav/lib/CalDAV/Calendar.php b/apps/dav/lib/CalDAV/Calendar.php
index a216e4e078..9c56398b14 100644
--- a/apps/dav/lib/CalDAV/Calendar.php
+++ b/apps/dav/lib/CalDAV/Calendar.php
@@ -145,11 +145,16 @@ class Calendar extends \Sabre\CalDAV\Calendar implements IShareable {
 			];
 		}
 
-		if ($this->isShared()) {
+		$acl = $this->caldavBackend->applyShareAcl($this->getResourceId(), $acl);
+
+		if (!$this->isShared()) {
 			return $acl;
 		}
 
-		return $this->caldavBackend->applyShareAcl($this->getResourceId(), $acl);
+		$allowedPrincipals = [$this->getOwner(), parent::getOwner(), 'principals/system/public'];
+		return array_filter($acl, function($rule) use ($allowedPrincipals) {
+			return in_array($rule['principal'], $allowedPrincipals);
+		});
 	}
 
 	public function getChildACL() {
diff --git a/apps/dav/tests/unit/CalDAV/CalendarTest.php b/apps/dav/tests/unit/CalDAV/CalendarTest.php
index 4ede886d31..cf295f0106 100644
--- a/apps/dav/tests/unit/CalDAV/CalendarTest.php
+++ b/apps/dav/tests/unit/CalDAV/CalendarTest.php
@@ -246,6 +246,7 @@ class CalendarTest extends TestCase {
 			]);
 		$backend->expects($this->any())->method('getCalendarObject')
 			->willReturn($calObject2)->with(666, 'event-2');
+		$backend->expects($this->any())->method('applyShareAcl')->willReturnArgument(1);
 
 		$calendarInfo = [
 			'principaluri' => 'user2',
@@ -333,6 +334,7 @@ EOD;
 			]);
 		$backend->expects($this->any())->method('getCalendarObject')
 			->willReturn($calObject1)->with(666, 'event-1');
+		$backend->expects($this->any())->method('applyShareAcl')->willReturnArgument(1);
 
 		$calendarInfo = [
 			'{http://owncloud.org/ns}owner-principal' => $isShared ? 'user1' : 'user2',
diff --git a/apps/dav/tests/unit/CalDAV/PublicCalendarTest.php b/apps/dav/tests/unit/CalDAV/PublicCalendarTest.php
index 6b2bf58d39..03cbf71d6c 100644
--- a/apps/dav/tests/unit/CalDAV/PublicCalendarTest.php
+++ b/apps/dav/tests/unit/CalDAV/PublicCalendarTest.php
@@ -51,6 +51,7 @@ class PublicCalendarTest extends CalendarTest {
 			]);
 		$backend->expects($this->any())->method('getCalendarObject')
 			->willReturn($calObject2)->with(666, 'event-2');
+		$backend->expects($this->any())->method('applyShareAcl')->willReturnArgument(1);
 
 		$calendarInfo = [
 			'{http://owncloud.org/ns}owner-principal' => 'user2',
@@ -135,6 +136,7 @@ EOD;
 			]);
 		$backend->expects($this->any())->method('getCalendarObject')
 			->willReturn($calObject1)->with(666, 'event-1');
+		$backend->expects($this->any())->method('applyShareAcl')->willReturnArgument(1);
 
 		$calendarInfo = [
 			'{http://owncloud.org/ns}owner-principal' => 'user1',