diff --git a/passes/techmap/Makefile.inc b/passes/techmap/Makefile.inc
index ba365525..2e90215e 100644
--- a/passes/techmap/Makefile.inc
+++ b/passes/techmap/Makefile.inc
@@ -3,8 +3,10 @@ GENFILES += passes/techmap/stdcells.inc
 OBJS += passes/techmap/techmap.o
 
 passes/techmap/stdcells.inc: techlibs/stdcells.v
+	echo -n "// autogenerated from $< on " > $@.new
+	LANG=C date >> $@.new
 	od -v -td1 -w1 $< | awk 'BEGIN { print "static char stdcells_code[] = {"; } $$2 != "" { print $$2 ","; } \
-			END { print 0 "};"; }' | fmt > $@.new
+			END { print 0 "};"; }' | fmt >> $@.new
 	mv $@.new $@
 
 passes/techmap/techmap.o: passes/techmap/stdcells.inc