diff --git a/targets/TARGET_STM/TARGET_STM32F1/serial_device.c b/targets/TARGET_STM/TARGET_STM32F1/serial_device.c
index eb7a66b7063..6902da9672c 100644
--- a/targets/TARGET_STM/TARGET_STM32F1/serial_device.c
+++ b/targets/TARGET_STM/TARGET_STM32F1/serial_device.c
@@ -32,7 +32,11 @@
 
 #include "serial_api_hal.h"
 
+#if defined(TARGET_STM32F103xG)
+#define UART_NUM (5)
+#else
 #define UART_NUM (3)
+#endif
 
 uint32_t serial_irq_ids[UART_NUM] = {0};
 UART_HandleTypeDef uart_handlers[UART_NUM];
@@ -94,6 +98,20 @@ static void uart3_irq(void)
 }
 #endif
 
+#if defined(USART4_BASE)
+static void uart4_irq(void)
+{
+    uart_irq(UART_4);
+}
+#endif
+
+#if defined(USART5_BASE)
+static void uart5_irq(void)
+{
+    uart_irq(UART_5);
+}
+#endif
+
 void serial_irq_handler(serial_t *obj, uart_irq_handler handler, uint32_t id)
 {
     struct serial_s *obj_s = SERIAL_S(obj);
@@ -130,6 +148,20 @@ void serial_irq_set(serial_t *obj, SerialIrq irq, uint32_t enable)
     }
 #endif
 
+#if defined(USART4_BASE)
+    if (obj_s->uart == UART_4) {
+        irq_n = USART4_IRQn;
+        vector = (uint32_t)&uart4_irq;
+    }
+#endif
+
+#if defined(USART5_BASE)
+    if (obj_s->uart == UART_5) {
+        irq_n = USART5_IRQn;
+        vector = (uint32_t)&uart5_irq;
+    }
+#endif
+
     if (enable) {
         if (irq == RxIrq) {
             __HAL_UART_ENABLE_IT(huart, UART_IT_RXNE);
@@ -302,6 +334,16 @@ static IRQn_Type serial_get_irq_n(UARTName uart_name)
         case UART_3:
             irq_n = USART3_IRQn;
             break;
+#endif
+#if defined(USART4_BASE)
+        case UART_4:
+            irq_n = USART4_IRQn;
+            break;
+#endif
+#if defined(USART5_BASE)
+        case UART_5:
+            irq_n = USART5_IRQn;
+            break;
 #endif
         default:
             irq_n = (IRQn_Type)0;