diff --git a/usr.bin/diff/tests/Makefile b/usr.bin/diff/tests/Makefile
index 4dfa372f2c4d..295e3141f3d9 100644
--- a/usr.bin/diff/tests/Makefile
+++ b/usr.bin/diff/tests/Makefile
@@ -1,37 +1,38 @@
 # $FreeBSD$
 
 PACKAGE=	tests
 
 ATF_TESTS_SH=	diff_test
 
 ${PACKAGE}FILES+=	\
 	input1.in \
 	input2.in \
 	input_c1.in \
 	input_c2.in \
 	simple.out \
 	simple_e.out \
 	simple_n.out \
 	simple_u.out \
 	simple_i.out \
 	simple_w.out \
 	simple_b.out \
 	simple_p.out \
 	unified_p.out \
 	unified_c9999.out \
 	unified_9999.out \
 	header.out \
-	header_ns.out
+	header_ns.out \
+	ifdef.out
 
 NETBSD_ATF_TESTS_SH+=	netbsd_diff_test
 
 ${PACKAGE}FILES+=	\
 	d_mallocv1.in	\
 	d_mallocv2.in
 
 ATF_TESTS_SH_SED_netbsd_diff_test+=	-e 's,t_diff,netbsd_diff_test,g'
 ATF_TESTS_SH_SRC_netbsd_diff_test=	t_diff.sh
 
 .include <netbsd-tests.test.mk>
 
 .include <bsd.test.mk>
diff --git a/usr.bin/diff/tests/diff_test.sh b/usr.bin/diff/tests/diff_test.sh
index c712d5871480..589bc9a8603b 100755
--- a/usr.bin/diff/tests/diff_test.sh
+++ b/usr.bin/diff/tests/diff_test.sh
@@ -1,79 +1,88 @@
 # $FreeBSD$
 
 atf_test_case simple
 atf_test_case unified
 atf_test_case header
 atf_test_case header_ns
+atf_test_case ifdef
 
 simple_body()
 {
 	atf_check -o file:$(atf_get_srcdir)/simple.out -s eq:1 \
 		diff "$(atf_get_srcdir)/input1.in" "$(atf_get_srcdir)/input2.in"
 
 	atf_check -o file:$(atf_get_srcdir)/simple_e.out -s eq:1 \
 		diff -e "$(atf_get_srcdir)/input1.in" "$(atf_get_srcdir)/input2.in"
 
 	atf_check -o file:$(atf_get_srcdir)/simple_u.out -s eq:1 \
 		diff -u -L input1 -L input2 "$(atf_get_srcdir)/input1.in" "$(atf_get_srcdir)/input2.in"
 
 	atf_check -o file:$(atf_get_srcdir)/simple_n.out -s eq:1 \
 		diff -n "$(atf_get_srcdir)/input1.in" "$(atf_get_srcdir)/input2.in"
 
 	atf_check -o inline:"Files $(atf_get_srcdir)/input1.in and $(atf_get_srcdir)/input2.in differ\n" -s eq:1 \
 		diff -q "$(atf_get_srcdir)/input1.in" "$(atf_get_srcdir)/input2.in"
 
 	atf_check \
 		diff -q "$(atf_get_srcdir)/input1.in" "$(atf_get_srcdir)/input1.in"
 
 	atf_check -o file:$(atf_get_srcdir)/simple_i.out -s eq:1 \
 		diff -i "$(atf_get_srcdir)/input_c1.in" "$(atf_get_srcdir)/input_c2.in"
 
 	atf_check -o file:$(atf_get_srcdir)/simple_w.out -s eq:1 \
 		diff -w "$(atf_get_srcdir)/input_c1.in" "$(atf_get_srcdir)/input_c2.in"
 
 	atf_check -o file:$(atf_get_srcdir)/simple_b.out -s eq:1 \
 		diff -b "$(atf_get_srcdir)/input_c1.in" "$(atf_get_srcdir)/input_c2.in"
 
 	atf_check -o file:$(atf_get_srcdir)/simple_p.out -s eq:1 \
 		diff --label input_c1.in --label input_c2.in -p "$(atf_get_srcdir)/input_c1.in" "$(atf_get_srcdir)/input_c2.in"
 }
 
 unified_body()
 {
 	atf_check -o file:$(atf_get_srcdir)/unified_p.out -s eq:1 \
 		diff -up -L input_c1.in -L input_c2.in  "$(atf_get_srcdir)/input_c1.in" "$(atf_get_srcdir)/input_c2.in"
 	atf_check -o file:$(atf_get_srcdir)/unified_c9999.out -s eq:1 \
 		diff -u -c9999 -L input_c1.in -L input_c2.in "$(atf_get_srcdir)/input_c1.in" "$(atf_get_srcdir)/input_c2.in"
 	atf_check -o file:$(atf_get_srcdir)/unified_9999.out -s eq:1 \
 		diff -u9999 -L input_c1.in -L input_c2.in "$(atf_get_srcdir)/input_c1.in" "$(atf_get_srcdir)/input_c2.in"
 }
 
 header_body()
 {
 	export TZ=UTC
 	: > empty
 	echo hello > hello
 	touch -d 2015-04-03T01:02:03 empty
 	touch -d 2016-12-22T11:22:33 hello
 	atf_check -o "file:$(atf_get_srcdir)/header.out" -s eq:1 \
 		diff -u empty hello
 }
 
 header_ns_body()
 {
 	export TZ=UTC
 	: > empty
 	echo hello > hello
 	touch -d 2015-04-03T01:02:03.123456789 empty
 	touch -d 2016-12-22T11:22:33.987654321 hello
 	atf_check -o "file:$(atf_get_srcdir)/header_ns.out" -s eq:1 \
 		diff -u empty hello
 }
 
+ifdef_body()
+{
+	atf_check -o file:$(atf_get_srcdir)/ifdef.out -s eq:1 \
+		diff -D PLOP "$(atf_get_srcdir)/input_c1.in" \
+		"$(atf_get_srcdir)/input_c2.in"
+}
+
 atf_init_test_cases()
 {
 	atf_add_test_case simple
 	atf_add_test_case unified
 	atf_add_test_case header
 	atf_add_test_case header_ns
+	atf_add_test_case ifdef
 }
diff --git a/usr.bin/diff/tests/ifdef.out b/usr.bin/diff/tests/ifdef.out
new file mode 100644
index 000000000000..cc72cac08635
--- /dev/null
+++ b/usr.bin/diff/tests/ifdef.out
@@ -0,0 +1,26 @@
+/*
+ * A comment 
+ *
+#ifndef PLOP
+ * And another  bla
+#else /* PLOP */
+ * And another bla
+#endif /* PLOP */
+ *
+#ifndef PLOP
+ * And yet another
+#else /* PLOP */
+ * and yet another
+#endif /* PLOP */
+ */
+
+int
+main(void)
+{
+#ifdef PLOP
+
+#endif /* PLOP */
+	printf("something");
+
+	return (0);
+}