diff --git a/plot/plotRutils.c b/plot/plotRutils.c
index 821567a5..35fcce50 100644
--- a/plot/plotRutils.c
+++ b/plot/plotRutils.c
@@ -519,7 +519,7 @@ PlotDumpRaster(raster, file)
     int count;
 
     count = write(fileno(file), (char *) raster->ras_bits,
-	    raster->ras_bytesPerLine*raster->ras_height);
+	    (size_t)raster->ras_bytesPerLine * raster->ras_height);
     if (count < 0)
     {
 	TxError("I/O error in writing raster file:  %s.\n",