diff --git a/lib/private/Preview/Office.php b/lib/private/Preview/Office.php
index fef218823e21d..50c016737ece9 100644
--- a/lib/private/Preview/Office.php
+++ b/lib/private/Preview/Office.php
@@ -74,7 +74,7 @@ public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
 		}
 
 		$image = new \OC_Image();
-		$image->loadFromData($png);
+		$image->loadFromData((string) $png);
 
 		$this->cleanTmpFiles();
 		unlink($pngPreview);