diff --git a/WHENCE b/WHENCE
index ef51ac11..3b9f5e29 100644
--- a/WHENCE
+++ b/WHENCE
@@ -173,6 +173,8 @@ Source: keyspan_pda/keyspan_pda.S
 File: keyspan_pda/xircom_pgs.fw
 Source: keyspan_pda/xircom_pgs.S
 
+Source: keyspan_pda/Makefile
+
 Licence: GPLv2+
 
 Compiled from original 8051 source into Intel HEX, used in our binary ihex form.
diff --git a/keyspan_pda/Makefile b/keyspan_pda/Makefile
new file mode 100644
index 00000000..fc37ea48
--- /dev/null
+++ b/keyspan_pda/Makefile
@@ -0,0 +1,12 @@
+CC = gcc
+IHEX2FW = ihex2fw
+
+all: keyspan_pda.fw xircom_pgs.fw
+
+%.fw: %.S
+	$(CC) -x assembler-with-cpp -P -E -o $*.asm $<
+	as31 -l $*.asm
+	$(IHEX2FW) $*.hex $@
+
+clean:
+	rm -f *.asm *.fw *.hex *.lst *.obj