diff --git a/drivers/tty/serial/stm32-usart.h b/drivers/tty/serial/stm32-usart.h
index 8cecfdce9386..5ce1d3aae07e 100644
--- a/drivers/tty/serial/stm32-usart.h
+++ b/drivers/tty/serial/stm32-usart.h
@@ -183,7 +183,7 @@ struct stm32_usart_info {
 #define USART_PRESC_MAX		0b1011
 
 #define STM32_SERIAL_NAME "ttySTM"
-#define STM32_MAX_PORTS 8
+#define STM32_MAX_PORTS 9
 
 #define RX_BUF_L 4096		 /* dma rx buffer length     */
 #define RX_BUF_P (RX_BUF_L / 2)	 /* dma rx buffer period     */