diff --git a/docs/examples/tristate/Makefile b/docs/examples/tristate/Makefile
new file mode 100644
index 0000000..1173566
--- /dev/null
+++ b/docs/examples/tristate/Makefile
@@ -0,0 +1,3 @@
+SUBDIR=../docs/examples/tristate
+TESTDIR=../../../tests
+include $(TESTDIR)/make/subdir.mk