diff --git a/tools/testing/selftests/clone3/Makefile b/tools/testing/selftests/clone3/Makefile
index cf976c732906..a7c7d8d15e1c 100644
--- a/tools/testing/selftests/clone3/Makefile
+++ b/tools/testing/selftests/clone3/Makefile
@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
-CFLAGS += -g -I../../../../usr/include/
+CFLAGS += -Wall -g -I../../../../usr/include/
 
 TEST_GEN_PROGS := clone3 clone3_clear_sighand clone3_set_tid
 
diff --git a/tools/testing/selftests/clone3/clone3_set_tid.c b/tools/testing/selftests/clone3/clone3_set_tid.c
index 3480e1c46983..ab1df5ce201f 100644
--- a/tools/testing/selftests/clone3/clone3_set_tid.c
+++ b/tools/testing/selftests/clone3/clone3_set_tid.c
@@ -30,6 +30,12 @@
 static int pipe_1[2];
 static int pipe_2[2];
 
+static void flush()
+{
+	fflush(stdout);
+	fflush(stderr);
+}
+
 static int call_clone3_set_tid(pid_t *set_tid,
 			       size_t set_tid_size,
 			       int flags,
@@ -46,6 +52,7 @@ static int call_clone3_set_tid(pid_t *set_tid,
 		.set_tid_size = set_tid_size,
 	};
 
+	flush();
 	pid = sys_clone3(&args, sizeof(struct clone_args));
 	if (pid < 0) {
 		ksft_print_msg("%s - Failed to create new process\n",
@@ -83,6 +90,7 @@ static int call_clone3_set_tid(pid_t *set_tid,
 			close(pipe_2[0]);
 		}
 
+		flush();
 		if (set_tid[0] != getpid())
 			_exit(EXIT_FAILURE);
 		_exit(exit_code);
@@ -153,7 +161,7 @@ int main(int argc, char *argv[])
 		ksft_exit_fail_msg("pipe() failed\n");
 
 	ksft_print_header();
-	ksft_set_plan(27);
+	ksft_set_plan(29);
 
 	f = fopen("/proc/sys/kernel/pid_max", "r");
 	if (f == NULL)
@@ -249,6 +257,7 @@ int main(int argc, char *argv[])
 	pid = fork();
 	if (pid == 0) {
 		ksft_print_msg("Child has PID %d\n", getpid());
+		flush();
 		_exit(EXIT_SUCCESS);
 	}
 	if (waitpid(pid, &status, 0) < 0)
@@ -283,6 +292,19 @@ int main(int argc, char *argv[])
 	/* Let's create a PID 1 */
 	ns_pid = fork();
 	if (ns_pid == 0) {
+		set_tid[0] = 43;
+		set_tid[1] = -1;
+		/*
+		 * This should fail as there are not enough active PID
+		 * namespaces. Again assuming this is running in the host's
+		 * PID namespace. Not yet nested.
+		 */
+		test_clone3_set_tid(set_tid, 2, 0, -EINVAL, 0, 0);
+
+		set_tid[0] = 43;
+		set_tid[1] = pid;
+		test_clone3_set_tid(set_tid, 2, 0, 0, 43, 0);
+
 		ksft_print_msg("Child in PID namespace has PID %d\n", getpid());
 		set_tid[0] = 2;
 		test_clone3_set_tid(set_tid, 1, 0, 0, 2, 0);
@@ -309,6 +331,8 @@ int main(int argc, char *argv[])
 		 */
 		test_clone3_set_tid(set_tid, 3, CLONE_NEWPID, 0, 42, true);
 
+
+		flush();
 		_exit(ksft_cnt.ksft_pass);
 	}