diff --git a/spice/qxl_dev.h b/spice/qxl_dev.h
index c844d7b..3f56aae 100644
--- a/spice/qxl_dev.h
+++ b/spice/qxl_dev.h
@@ -740,6 +740,9 @@ typedef struct SPICE_ATTR_PACKED QXLSurfaceId {
 
 typedef struct SPICE_ATTR_PACKED QXLQUICData {
     uint32_t data_size;
+    /* This data for QUIC is a QXLDataChunk.
+     * This differs from QXLBitmap where it's a reference to bitmap data or
+     * a reference to QXLDataChunk */
     uint8_t data[0];
 } QXLQUICData, QXLLZRGBData, QXLJPEGData;