diff --git a/Libs/DICOM/Widgets/ctkDICOMThumbnailGenerator.cpp b/Libs/DICOM/Widgets/ctkDICOMThumbnailGenerator.cpp
index 3439f3d1b0..a99ee51705 100644
--- a/Libs/DICOM/Widgets/ctkDICOMThumbnailGenerator.cpp
+++ b/Libs/DICOM/Widgets/ctkDICOMThumbnailGenerator.cpp
@@ -171,7 +171,7 @@ bool ctkDICOMThumbnailGenerator::generateThumbnail(DicomImage *dcmImage, QImage&
   /* create output buffer for DicomImage class */
   QByteArray buffer;
   /* copy header to output buffer and resize it for pixel data */
-  buffer.append(header);
+  buffer.append(header.toUtf8());
   buffer.resize(length);
 
   /* render pixel data to buffer */