--- /var/tmp/portage/netpbm-10.29/work/netpbm-10.29/converter/other/pnmtopng.c	2005-08-06 17:26:55.000000000 +0000
+++ pnmtopng.c	2005-09-06 00:40:14.000000000 +0000
@@ -1690,7 +1690,8 @@
             pnm_promoteformatrow(xelrow, cols, maxval, format, maxval,
                                  PPM_TYPE);
             
-            makePngLine(line, xelrow, cols, maxval, alpha, alpha_mask[row],
+            makePngLine(line, xelrow, cols, maxval, 
+			alpha, alpha ? alpha_mask[row] : NULL,
                         cht, caht, info_ptr, png_maxval, depth);
 
             png_write_row(png_ptr, line);