diff --git a/common/rfb/JpegCompressor.h b/common/rfb/JpegCompressor.h
index 798572e..d50e587 100644
--- a/common/rfb/JpegCompressor.h
+++ b/common/rfb/JpegCompressor.h
@@ -51,7 +51,7 @@
     JpegCompressor(int bufferLen = 128*1024);
     virtual ~JpegCompressor();
 
-    void compress(rdr::U8 *, int, const Rect&, const PixelFormat&, int,
+    void compress(const rdr::U8 *, int, const Rect&, const PixelFormat&, int,
       JPEG_SUBSAMP);
 
     void writeBytes(const void*, int);