diff --git a/common/rfb/SMsgWriter.cxx b/common/rfb/SMsgWriter.cxx
index 1a02ce3..a8b9c29 100644
--- a/common/rfb/SMsgWriter.cxx
+++ b/common/rfb/SMsgWriter.cxx
@@ -105,7 +105,8 @@
 
   encoders[encoding]->setCompressLevel(cp->compressLevel);
   encoders[encoding]->setQualityLevel(cp->qualityLevel);
-  jpegEncoder->setQualityLevel(cp->qualityLevel);
+  if (cp->qualityLevel != -1)
+    jpegEncoder->setQualityLevel(cp->qualityLevel);
 }
 
 int SMsgWriter::getNumRects(const Rect &r)
@@ -175,7 +176,7 @@
 
 bool SMsgWriter::canUseJpegEncoder(PixelBuffer *pb) const
 {
-  return jpegEncoder->isPixelFormatSupported(pb);
+  return (cp->qualityLevel != -1 && jpegEncoder->isPixelFormatSupported(pb));
 }
 
 void SMsgWriter::writeJpegRect(PixelBuffer *pb, const Rect& r)