diff --git a/lib/posix/pthread.c b/lib/posix/pthread.c
index fa08f5f53e7..3a21d373989 100644
--- a/lib/posix/pthread.c
+++ b/lib/posix/pthread.c
@@ -227,7 +227,8 @@ static bool is_posix_policy_prio_valid(uint32_t priority, int policy)
 	return false;
 }
 
-static int zephyr_to_posix_priority(int z_prio, int *policy)
+/* Non-static so that they can be tested in ztest */
+int zephyr_to_posix_priority(int z_prio, int *policy)
 {
 	if (z_prio < 0) {
 		__ASSERT_NO_MSG(-z_prio <= CONFIG_NUM_COOP_PRIORITIES);
@@ -239,7 +240,8 @@ static int zephyr_to_posix_priority(int z_prio, int *policy)
 	return ZEPHYR_TO_POSIX_PRIORITY(z_prio);
 }
 
-static int posix_to_zephyr_priority(int priority, int policy)
+/* Non-static so that they can be tested in ztest */
+int posix_to_zephyr_priority(int priority, int policy)
 {
 	if (policy == SCHED_FIFO) {
 		/* COOP: highest [-CONFIG_NUM_COOP_PRIORITIES, -1] lowest */
diff --git a/tests/posix/common/src/pthread.c b/tests/posix/common/src/pthread.c
index feab8d64d59..d4038eba629 100644
--- a/tests/posix/common/src/pthread.c
+++ b/tests/posix/common/src/pthread.c
@@ -215,6 +215,39 @@ static void *thread_top_term(void *p1)
 	return NULL;
 }
 
+/* Test the internal priority conversion functions */
+int zephyr_to_posix_priority(int z_prio, int *policy);
+int posix_to_zephyr_priority(int priority, int policy);
+ZTEST(pthread, test_pthread_priority_conversion)
+{
+	/*
+	 *    ZEPHYR [-CONFIG_NUM_COOP_PRIORITIES, -1]
+	 *                       TO
+	 * POSIX(FIFO) [0, CONFIG_NUM_COOP_PRIORITIES - 1]
+	 */
+	for (int z_prio = -CONFIG_NUM_COOP_PRIORITIES, prio = CONFIG_NUM_COOP_PRIORITIES - 1,
+		 p_prio, policy;
+	     z_prio <= -1; z_prio++, prio--) {
+		p_prio = zephyr_to_posix_priority(z_prio, &policy);
+		zassert_equal(policy, SCHED_FIFO);
+		zassert_equal(p_prio, prio, "%d %d\n", p_prio, prio);
+		zassert_equal(z_prio, posix_to_zephyr_priority(p_prio, SCHED_FIFO));
+	}
+
+	/*
+	 *  ZEPHYR [0, CONFIG_NUM_PREEMPT_PRIORITIES - 1]
+	 *                      TO
+	 * POSIX(RR) [0, CONFIG_NUM_PREEMPT_PRIORITIES - 1]
+	 */
+	for (int z_prio = 0, prio = CONFIG_NUM_PREEMPT_PRIORITIES - 1, p_prio, policy;
+	     z_prio < CONFIG_NUM_PREEMPT_PRIORITIES; z_prio++, prio--) {
+		p_prio = zephyr_to_posix_priority(z_prio, &policy);
+		zassert_equal(policy, SCHED_RR);
+		zassert_equal(p_prio, prio, "%d %d\n", p_prio, prio);
+		zassert_equal(z_prio, posix_to_zephyr_priority(p_prio, SCHED_RR));
+	}
+}
+
 ZTEST(pthread, test_pthread_execution)
 {
 	int i, ret;