Index: usr.bin/diff/diffreg.c
===================================================================
--- usr.bin/diff/diffreg.c
+++ usr.bin/diff/diffreg.c
@@ -1614,7 +1614,7 @@
 	char buf2[256];
 	char end1[10];
 	char end2[10];
-	struct tm *tm_ptr1, *tm_ptr2;
+	struct tm tm1, tm2, *tm_ptr1, *tm_ptr2;
 	int nsec1 = TIMESPEC_NS (stb1.st_mtime);
 	int nsec2 = TIMESPEC_NS (stb2.st_mtime);
 
@@ -1626,8 +1626,8 @@
 
 	if (cflag)
 		time_format = "%c";
-	tm_ptr1 = localtime(&stb1.st_mtime);
-	tm_ptr2 = localtime(&stb2.st_mtime);
+	tm_ptr1 = localtime_r(&stb1.st_mtime, &tm1);
+	tm_ptr2 = localtime_r(&stb2.st_mtime, &tm2);
 	strftime(buf1, 256, time_format, tm_ptr1);
 	strftime(buf2, 256, time_format, tm_ptr2);
 	if (!cflag) {
Index: usr.bin/diff/tests/Makefile
===================================================================
--- usr.bin/diff/tests/Makefile
+++ usr.bin/diff/tests/Makefile
@@ -19,7 +19,8 @@
 	simple_p.out \
 	unified_p.out \
 	unified_c9999.out \
-	unified_9999.out
+	unified_9999.out \
+	header.out
 
 NETBSD_ATF_TESTS_SH+=	netbsd_diff_test
 
Index: usr.bin/diff/tests/diff_test.sh
===================================================================
--- usr.bin/diff/tests/diff_test.sh
+++ usr.bin/diff/tests/diff_test.sh
@@ -2,6 +2,7 @@
 
 atf_test_case simple
 atf_test_case unified
+atf_test_case header
 
 simple_body()
 {
@@ -46,8 +47,20 @@
 		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
+}
+
 atf_init_test_cases()
 {
 	atf_add_test_case simple
 	atf_add_test_case unified
+	atf_add_test_case header
 }
Index: usr.bin/diff/tests/header.out
===================================================================
--- /dev/null
+++ usr.bin/diff/tests/header.out
@@ -0,0 +1,4 @@
+--- empty	2015-04-03 01:02:03.000000000 +0000
++++ hello	2016-12-22 11:22:33.000000000 +0000
+@@ -0,0 +1 @@
++hello