diff --git a/usr.bin/cmp/cmp.c b/usr.bin/cmp/cmp.c
--- a/usr.bin/cmp/cmp.c
+++ b/usr.bin/cmp/cmp.c
@@ -92,6 +92,13 @@
 	return (true);
 }
 
+static void
+check_stdout(void)
+{
+	if (fflush(stdout) != 0)
+		err(ERR_EXIT, "stdout");
+}
+
 int
 main(int argc, char *argv[])
 {
@@ -197,6 +204,8 @@
 	if (sflag && skip1 == 0 && skip2 == 0)
 		zflag = true;
 
+	atexit(check_stdout);
+
 	if (fd1 == -1) {
 		if (fd2 == -1) {
 			c_link(file1, skip1, file2, skip2, limit);
diff --git a/usr.bin/cmp/tests/cmp_test2.sh b/usr.bin/cmp/tests/cmp_test2.sh
--- a/usr.bin/cmp/tests/cmp_test2.sh
+++ b/usr.bin/cmp/tests/cmp_test2.sh
@@ -133,6 +133,24 @@
 	    cmp -bl a b
 }
 
+atf_test_case stdout
+stdout_head()
+{
+	atf_set descr "Failure to write to stdout"
+}
+stdout_body()
+{
+	echo a >a
+	echo b >b
+	(
+		trap "" PIPE
+		cmp a b 2>stderr
+		echo $? >result
+	) | true
+	atf_check -o inline:"2\n" cat result
+	atf_check -o match:"stdout" cat stderr
+}
+
 atf_init_test_cases()
 {
 	atf_add_test_case special
@@ -141,4 +159,5 @@
 	atf_add_test_case skipsuff
 	atf_add_test_case limit
 	atf_add_test_case bflag
+	atf_add_test_case stdout
 }