diff --git a/tools/rgb2ycbcr.c b/tools/rgb2ycbcr.c
index a2771757..ff8846d1 100644
--- a/tools/rgb2ycbcr.c
+++ b/tools/rgb2ycbcr.c
@@ -1,4 +1,4 @@
-/* $Header: /cvs/maptools/cvsroot/libtiff/tools/rgb2ycbcr.c,v 1.3 1999-12-27 17:35:01 mwelles Exp $ */
+/* $Header: /cvs/maptools/cvsroot/libtiff/tools/rgb2ycbcr.c,v 1.4 2000-10-19 13:23:49 warmerda Exp $ */
 
 /*
  * Copyright (c) 1991-1997 Sam Leffler
@@ -241,9 +241,10 @@ cvtRaster(TIFF* tif, uint32* raster, uint32 width, uint32 height)
 	uint32 rwidth = roundup(width, horizSubSampling);
 	uint32 rheight = roundup(height, vertSubSampling);
 	uint32 nrows = (rowsperstrip > rheight ? rheight : rowsperstrip);
+        uint32 rnrows = roundup(nrows,vertSubSampling);
 
-	cc = nrows*rwidth +
-	    2*((nrows*rwidth) / (horizSubSampling*vertSubSampling));
+	cc = rnrows*rwidth +
+	    2*((rnrows*rwidth) / (horizSubSampling*vertSubSampling));
 	buf = (unsigned char*)_TIFFmalloc(cc);
 	for (y = height; (int32) y > 0; y -= nrows) {
 		uint32 nr = (y > nrows ? nrows : y);