diff --git a/apps/files_trashbin/lib/Sabre/TrashbinPlugin.php b/apps/files_trashbin/lib/Sabre/TrashbinPlugin.php
index 36237ca080b..54bb1326966 100644
--- a/apps/files_trashbin/lib/Sabre/TrashbinPlugin.php
+++ b/apps/files_trashbin/lib/Sabre/TrashbinPlugin.php
@@ -104,8 +104,8 @@ class TrashbinPlugin extends ServerPlugin {
 			return $node->getFileId();
 		});
 
-		$propFind->handle(FilesPlugin::HAS_PREVIEW_PROPERTYNAME, function () use ($node) {
-			return $this->previewManager->isAvailable($node->getFileInfo());
+		$propFind->handle(FilesPlugin::HAS_PREVIEW_PROPERTYNAME, function () use ($node): string {
+			return $this->previewManager->isAvailable($node->getFileInfo()) ? 'true' : 'false';
 		});
 
 		$propFind->handle(FilesPlugin::MOUNT_TYPE_PROPERTYNAME, function () {
diff --git a/apps/files_versions/lib/Sabre/Plugin.php b/apps/files_versions/lib/Sabre/Plugin.php
index 4b4cb0638bf..984c4a36e5b 100644
--- a/apps/files_versions/lib/Sabre/Plugin.php
+++ b/apps/files_versions/lib/Sabre/Plugin.php
@@ -82,7 +82,10 @@ class Plugin extends ServerPlugin {
 		if ($node instanceof VersionFile) {
 			$propFind->handle(self::VERSION_LABEL, fn () => $node->getMetadataValue(self::LABEL));
 			$propFind->handle(self::VERSION_AUTHOR, fn () => $node->getMetadataValue(self::AUTHOR));
-			$propFind->handle(FilesPlugin::HAS_PREVIEW_PROPERTYNAME, fn () => $this->previewManager->isMimeSupported($node->getContentType()));
+			$propFind->handle(
+				FilesPlugin::HAS_PREVIEW_PROPERTYNAME,
+				fn (): string => $this->previewManager->isMimeSupported($node->getContentType()) ? 'true' : 'false',
+			);
 		}
 	}