diff --git a/include/posix/pthread.h b/include/posix/pthread.h
index ce49e565f6c..267d05b59c5 100644
--- a/include/posix/pthread.h
+++ b/include/posix/pthread.h
@@ -334,6 +334,8 @@ static inline int pthread_mutexattr_destroy(pthread_mutexattr_t *m)
 		.max = count,					\
 	}
 
+#define PTHREAD_BARRIER_SERIAL_THREAD 1
+
 /**
  * @brief POSIX threading compatibility API
  *
diff --git a/lib/posix/pthread_barrier.c b/lib/posix/pthread_barrier.c
index e968031554d..d23f0e55774 100644
--- a/lib/posix/pthread_barrier.c
+++ b/lib/posix/pthread_barrier.c
@@ -11,10 +11,8 @@
 
 int pthread_barrier_wait(pthread_barrier_t *b)
 {
-	/* FIXME: This function should return PTHREAD_BARRIER_SERIAL_THREAD
-	 * for an arbitrary thread and 0 for the others.
-	 */
-	int key = irq_lock();
+	unsigned int key = irq_lock();
+	int ret = 0;
 
 	b->count++;
 
@@ -25,8 +23,10 @@ int pthread_barrier_wait(pthread_barrier_t *b)
 			_ready_one_thread(&b->wait_q);
 		}
 		_reschedule_irqlock(key);
-		return 0;
+		ret = PTHREAD_BARRIER_SERIAL_THREAD;
 	} else {
-		return _pend_curr_irqlock(key, &b->wait_q, K_FOREVER);
+		(void) _pend_curr_irqlock(key, &b->wait_q, K_FOREVER);
 	}
+
+	return ret;
 }
diff --git a/tests/posix/common/src/pthread.c b/tests/posix/common/src/pthread.c
index c2956803d18..dc9c374f99d 100644
--- a/tests/posix/common/src/pthread.c
+++ b/tests/posix/common/src/pthread.c
@@ -44,6 +44,7 @@ static int curr_bounce_thread;
 
 static int barrier_failed;
 static int barrier_done[N_THR_E];
+static int barrier_return[N_THR_E];
 
 /* First phase bounces execution between two threads using a condition
  * variable, continuously testing that no other thread is mucking with
@@ -138,7 +139,7 @@ void *thread_top_exec(void *p1)
 			sem_post(&main_sem);
 		}
 	}
-	pthread_barrier_wait(&barrier);
+	barrier_return[id] = pthread_barrier_wait(&barrier);
 	barrier_done[id] = 1;
 	sem_post(&main_sem);
 	pthread_exit(p1);
@@ -231,6 +232,7 @@ void test_posix_pthread_execution(void)
 	int schedpolicy = SCHED_FIFO;
 	void *retval, *stackaddr;
 	size_t stacksize;
+	int serial_threads = 0;
 
 	sem_init(&main_sem, 0, 1);
 	schedparam.sched_priority = CONFIG_NUM_COOP_PRIORITIES - 1;
@@ -346,6 +348,15 @@ void test_posix_pthread_execution(void)
 		pthread_join(newthread[i], &retval);
 	}
 
+	for (i = 0; i < N_THR_E; i++) {
+		if (barrier_return[i] == PTHREAD_BARRIER_SERIAL_THREAD) {
+			++serial_threads;
+		}
+	}
+
+	/* TESTPOINT: Check only one PTHREAD_BARRIER_SERIAL_THREAD returned. */
+	zassert_true(serial_threads == 1, "Bungled barrier return value(s)");
+
 	printk("Barrier test OK\n");
 }