diff --git a/.gitmodules b/.gitmodules
index 62a4d6b9..dae49934 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -13,3 +13,6 @@
 [submodule "tools/simh"]
 	path = tools/simh
 	url = https://github.com/simh/simh
+[submodule "tools/supdup"]
+	path = tools/supdup
+	url = https://github.com/PDP-10/supdup
diff --git a/Makefile b/Makefile
index 61698877..2f5a9388 100644
--- a/Makefile
+++ b/Makefile
@@ -21,7 +21,7 @@ SIMH=${PWD}/tools/simh/BIN/pdp10
 ITSTAR=${PWD}/tools/itstar/itstar
 WRITETAPE=${PWD}/tools/tapeutils/tapewrite
 
-all: out/rp0.dsk
+all: out/rp0.dsk tools/supdup/supdup
 
 out/rp0.dsk: build/simh/init out/minsys.tape out/salv.tape out/dskdmp.tape build/build.tcl out/sources.tape build/$(EMULATOR)/stamp
 	PATH=${PWD}/tools/simh/BIN:$$PATH expect -f build/$(EMULATOR)/build.tcl
@@ -79,5 +79,8 @@ $(ITSTAR):
 $(WRITETAPE):
 	cd tools/tapeutils; make
 
+tools/supdup/supdup:
+	cd tools/supdup; make
+
 clean:
 	rm -rf out start build/*/stamp
diff --git a/tools/supdup b/tools/supdup
new file mode 160000
index 00000000..d1b96169
--- /dev/null
+++ b/tools/supdup
@@ -0,0 +1 @@
+Subproject commit d1b961699630bb0b27a863ade5999d583beb5e73