diff --git a/common/rfb/JpegCompressor.cxx b/common/rfb/JpegCompressor.cxx
index f4b6ed1..b3c5f7c 100644
--- a/common/rfb/JpegCompressor.cxx
+++ b/common/rfb/JpegCompressor.cxx
@@ -141,7 +141,7 @@
   delete cinfo;
 }
 
-void JpegCompressor::compress(rdr::U8 *buf, int pitch, const Rect& r,
+void JpegCompressor::compress(const rdr::U8 *buf, int pitch, const Rect& r,
   const PixelFormat& pf, int quality, JPEG_SUBSAMP subsamp)
 {
   int w = r.width();