diff --git a/drivers/serial/uart_nrfx_uart.c b/drivers/serial/uart_nrfx_uart.c
index 172e8729976..c4b43df03f6 100644
--- a/drivers/serial/uart_nrfx_uart.c
+++ b/drivers/serial/uart_nrfx_uart.c
@@ -272,10 +272,14 @@ static void uart_nrfx_poll_out(const struct device *dev, unsigned char c)
 		while (atomic_cas((atomic_t *) lock,
 				  (atomic_val_t) 0,
 				  (atomic_val_t) 1) == false) {
-			/* k_sleep allows other threads to execute and finish
-			 * their transactions.
-			 */
-			k_msleep(1);
+			if (IS_ENABLED(CONFIG_MULTITHREADING)) {
+				/* k_sleep allows other threads to execute and finish
+				 * their transactions.
+				 */
+				k_msleep(1);
+			} else {
+				k_busy_wait(1000);
+			}
 			if (--safety_cnt == 0) {
 				break;
 			}
diff --git a/drivers/serial/uart_nrfx_uarte.c b/drivers/serial/uart_nrfx_uarte.c
index 3f438e5ba3b..14ac2a75e57 100644
--- a/drivers/serial/uart_nrfx_uarte.c
+++ b/drivers/serial/uart_nrfx_uarte.c
@@ -489,7 +489,9 @@ static int wait_tx_ready(const struct device *dev)
 
 			irq_unlock(key);
 		}
-		k_msleep(1);
+		if (IS_ENABLED(CONFIG_MULTITHREADING)) {
+			k_msleep(1);
+		}
 	} while (1);
 
 	return key;