diff --git a/sys/atari/unx2atar.sed b/sys/atari/unx2atar.sed
new file mode 100644
index 000000000..8d4433075
--- /dev/null
+++ b/sys/atari/unx2atar.sed
@@ -0,0 +1,23 @@
+: loop
+/\\$/N
+/\\$/b loop
+# for each line, append any continuation lines before trying to classify it
+/^	/ {
+# if it starts with a tab, it's meant for the shell, and we should think
+#  about reversing the slashes
+s;cd ../util;cd ..\\util;
+s;cd ../src;cd ..\\src;
+/librarian/ s;dat/options;dat\\options;
+/$(MAKE)/b
+/$(CC)/b
+s;/;\\;g
+}
+# unfortunately, we do not want to reverse *all* the slashes, as even the
+#  Atari make and gcc like forward ones, and it's messy to avoid the ones in
+#  sed addresses
+# so, flip the first one in e.g.
+# 	@( cd ../util ; $(MAKE) ../include/onames.h )
+# flip the librarian-related ones in dat/options
+# ignore other lines related to make and gcc
+# and flip any slashes left over, which include a number of UNIX-only things
+#  that we didn't need to do but don't hurt