diff --git a/apps/dav/lib/CalDAV/CalDavBackend.php b/apps/dav/lib/CalDAV/CalDavBackend.php
index e29749c596e21..e1cefc2b1167a 100644
--- a/apps/dav/lib/CalDAV/CalDavBackend.php
+++ b/apps/dav/lib/CalDAV/CalDavBackend.php
@@ -2203,6 +2203,11 @@ public function getCalendarObjectByUID($principalUri, $uid) {
 		$stmt->closeCursor();
 		if ($row) {
 			if ($row['principaluri'] != $principalUri) {
+				/**
+				 * This seeems to be a false positive: we have "use Sabre\Uri" and Uri\split() IS defined.
+				 *
+				 * @psalm-suppress UndefinedFunction
+				 */
 				[, $name] = Uri\split($row['principaluri']);
 				$calendarUri = $row['calendaruri'] . '_shared_by_' . $name;
 			} else {
diff --git a/apps/dav/lib/CalDAV/Schedule/Plugin.php b/apps/dav/lib/CalDAV/Schedule/Plugin.php
index 8045421b89896..67ca1c739be0f 100644
--- a/apps/dav/lib/CalDAV/Schedule/Plugin.php
+++ b/apps/dav/lib/CalDAV/Schedule/Plugin.php
@@ -167,6 +167,7 @@ public function calendarObjectChange(RequestInterface $request, ResponseInterfac
 			return;
 		}
 
+		/** @var Calendar $calendarNode */
 		$calendarNode = $this->server->tree->getNodeForPath($calendarPath);
 
 		// Original code in parent class:
@@ -180,13 +181,22 @@ public function calendarObjectChange(RequestInterface $request, ResponseInterfac
 			$calendarNode->getPrincipalURI()
 		);
 
+		/** @var VCalendar $oldObj */
 		if (!$isNew) {
+			/** @var \Sabre\CalDAV\CalendarObject $node */
 			$node = $this->server->tree->getNodeForPath($request->getPath());
 			$oldObj = Reader::read($node->get());
 		} else {
 			$oldObj = null;
 		}
 
+		/**
+		 * Sabre has several issues with faulty argument type specifications
+		 * in its doc-block comments. Passing null is ok here.
+		 *
+		 * @psalm-suppress PossiblyNullArgument
+		 * @psalm-suppress ArgumentTypeCoercion
+		 */
 		$this->processICalendarChange($oldObj, $vCal, $addresses, [], $modified);
 
 		if ($oldObj) {