diff -ur a/harness/Makefile b/harness/Makefile
--- a/harness/Makefile	2022-05-03 19:46:21.460000000 +0000
+++ b/harness/Makefile	2022-05-03 19:46:57.450000000 +0000
@@ -1,6 +1,6 @@
 # foo.
 TEST_SRCS:=$(shell find cases/ -name \*.t | sort -n -t/ -k2)
-EXTRAPROGS:=cases/8.p cases/10.p
+EXTRAPROGS:=cases/8.p cases/10.p cases/18.p
 PARTPROGS:=$(filter-out $(EXTRAPROGS), $(patsubst %.t,%.p,$(TEST_SRCS)))
 PROGS:=$(PARTPROGS) $(EXTRAPROGS)
 HARNESS_SRCS:=main.c