Index: grfspecial.c
===================================================================
--- grfspecial.c	(revision 613)
+++ grfspecial.c	(working copy)
@@ -1725,6 +1725,7 @@
 	uint16 data = 0;
 
 	check_length(len, 5, "ParamSet");
+	buf++;
 	target = grf_load_byte(&buf);
 	oper = grf_load_byte(&buf);
 	src1 = grf_load_byte(&buf);