diff --git a/drivers/serial/serial_test.c b/drivers/serial/serial_test.c
index 6879cb378af..d90ec2dc5f6 100644
--- a/drivers/serial/serial_test.c
+++ b/drivers/serial/serial_test.c
@@ -31,6 +31,7 @@ struct serial_vnd_data {
 	void *callback_data;
 #ifdef CONFIG_UART_INTERRUPT_DRIVEN
 	uart_irq_callback_user_data_t irq_isr;
+	void *irq_isr_user_data;
 	bool irq_rx_enabled;
 	bool irq_tx_enabled;
 #endif
@@ -80,7 +81,7 @@ static void irq_process(const struct device *dev)
 			LOG_ERR("no isr registered");
 			break;
 		}
-		data->irq_isr(dev, NULL);
+		data->irq_isr(dev, data->irq_isr_user_data);
 	};
 }
 
@@ -141,11 +142,6 @@ static void irq_callback_set(const struct device *dev, uart_irq_callback_user_da
 {
 	struct serial_vnd_data *data = dev->data;
 
-	/* Not implemented. Ok because `user_data` is always NULL in the current
-	 * implementation of core UART API.
-	 */
-	__ASSERT_NO_MSG(user_data == NULL);
-
 #if defined(CONFIG_UART_EXCLUSIVE_API_CALLBACKS) && defined(CONFIG_UART_ASYNC_API)
 	if (data->read_buf) {
 		LOG_ERR("Setting callback to NULL while asynchronous API is in use.");
@@ -155,6 +151,7 @@ static void irq_callback_set(const struct device *dev, uart_irq_callback_user_da
 #endif
 
 	data->irq_isr = cb;
+	data->irq_isr_user_data = user_data;
 	LOG_DBG("callback set");
 }