diff --git a/libraries/mbed/targets/cmsis/TARGET_STM/TARGET_STM32F1/stm32f1xx_hal_conf.h b/libraries/mbed/targets/cmsis/TARGET_STM/TARGET_STM32F1/stm32f1xx_hal_conf.h
index fae9ea4287..28c4558cde 100644
--- a/libraries/mbed/targets/cmsis/TARGET_STM/TARGET_STM32F1/stm32f1xx_hal_conf.h
+++ b/libraries/mbed/targets/cmsis/TARGET_STM/TARGET_STM32F1/stm32f1xx_hal_conf.h
@@ -121,7 +121,7 @@
 
    
 #if !defined  (LSE_STARTUP_TIMEOUT)
-  #define LSE_STARTUP_TIMEOUT    ((uint32_t)100)   /*!< Time out for LSE start up, in ms */
+  #define LSE_STARTUP_TIMEOUT    ((uint32_t)5000)   /*!< Time out for LSE start up, in ms */
 #endif /* HSE_STARTUP_TIMEOUT */
 
    
diff --git a/libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F1/TARGET_DISCO_F100RB/device.h b/libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F1/TARGET_DISCO_F100RB/device.h
index 57a7aa227d..2a485c0e17 100644
--- a/libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F1/TARGET_DISCO_F100RB/device.h
+++ b/libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F1/TARGET_DISCO_F100RB/device.h
@@ -48,6 +48,7 @@
 #define DEVICE_SPISLAVE         1
 
 #define DEVICE_RTC              1
+#define DEVICE_RTC_LSI          0
 
 #define DEVICE_PWMOUT           1
 
diff --git a/libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F1/TARGET_NUCLEO_F103RB/device.h b/libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F1/TARGET_NUCLEO_F103RB/device.h
index 57a7aa227d..2a485c0e17 100644
--- a/libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F1/TARGET_NUCLEO_F103RB/device.h
+++ b/libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F1/TARGET_NUCLEO_F103RB/device.h
@@ -48,6 +48,7 @@
 #define DEVICE_SPISLAVE         1
 
 #define DEVICE_RTC              1
+#define DEVICE_RTC_LSI          0
 
 #define DEVICE_PWMOUT           1
 
diff --git a/libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F1/rtc_api.c b/libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F1/rtc_api.c
index 423350b67d..50cb7286f5 100644
--- a/libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F1/rtc_api.c
+++ b/libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F1/rtc_api.c
@@ -46,6 +46,19 @@ void rtc_init(void)
 
     RtcHandle.Instance = RTC;
 
+#if !DEVICE_RTC_LSI
+    // Enable LSE Oscillator
+    RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_LSE;
+    RCC_OscInitStruct.PLL.PLLState   = RCC_PLL_NONE; // Mandatory, otherwise the PLL is reconfigured!
+    RCC_OscInitStruct.LSEState       = RCC_LSE_ON; // External 32.768 kHz clock on OSC_IN/OSC_OUT
+    RCC_OscInitStruct.LSIState       = RCC_LSI_OFF;
+    if (HAL_RCC_OscConfig(&RCC_OscInitStruct) == HAL_OK) { // Check if LSE has started correctly
+        // Connect LSE to RTC
+        __HAL_RCC_RTC_CONFIG(RCC_RTCCLKSOURCE_LSE);
+    } else {
+	    error("Cannot initialize RTC with LSE\n");
+    }
+#else
     // Enable Power clock
     __HAL_RCC_PWR_CLK_ENABLE();
 
@@ -55,27 +68,20 @@ void rtc_init(void)
     // Reset Backup domain
     __HAL_RCC_BACKUPRESET_FORCE();
     __HAL_RCC_BACKUPRESET_RELEASE();
-
-    // Enable LSE Oscillator
-    RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_LSE;
-    RCC_OscInitStruct.PLL.PLLState   = RCC_PLL_NONE; // Mandatory, otherwise the PLL is reconfigured!
-    RCC_OscInitStruct.LSEState       = RCC_LSE_ON; // External 32.768 kHz clock on OSC_IN/OSC_OUT
-    if (HAL_RCC_OscConfig(&RCC_OscInitStruct) == HAL_OK) {
-        // Connect LSE to RTC
-        __HAL_RCC_RTC_CONFIG(RCC_RTCCLKSOURCE_LSE);
-    } else {
-        // Enable LSI clock
-        RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_LSI | RCC_OSCILLATORTYPE_LSE;
-        RCC_OscInitStruct.PLL.PLLState   = RCC_PLL_NONE; // Mandatory, otherwise the PLL is reconfigured!
-        RCC_OscInitStruct.LSEState       = RCC_LSE_OFF;
-        RCC_OscInitStruct.LSIState       = RCC_LSI_ON;
-        if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK) {
-            error("RTC error: LSI clock initialization failed.");
-        }
-        // Connect LSI to RTC
-        __HAL_RCC_RTC_CONFIG(RCC_RTCCLKSOURCE_LSI);
-    }
-
+	
+	// Enable LSI clock
+	RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_LSI | RCC_OSCILLATORTYPE_LSE;
+	RCC_OscInitStruct.PLL.PLLState   = RCC_PLL_NONE; // Mandatory, otherwise the PLL is reconfigured!
+	RCC_OscInitStruct.LSEState       = RCC_LSE_OFF;
+	RCC_OscInitStruct.LSIState       = RCC_LSI_ON;
+	if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK) {
+		error("Cannot initialize RTC with LSI\n");
+	}
+	// Connect LSI to RTC
+	__HAL_RCC_RTC_CONFIG(RCC_RTCCLKSOURCE_LSI);
+	// This value is LSI typical value. To be measured precisely using a timer input capture for example.
+#endif
+	
     // Enable RTC
     __HAL_RCC_RTC_ENABLE();
 
@@ -88,6 +94,7 @@ void rtc_init(void)
 
 void rtc_free(void)
 {
+#if DEVICE_RTC_LSI
     // Enable Power clock
     __PWR_CLK_ENABLE();
 
@@ -100,6 +107,7 @@ void rtc_free(void)
 
     // Disable access to Backup domain
     HAL_PWR_DisableBkUpAccess();
+#endif
 
     // Disable LSI and LSE clocks
     RCC_OscInitTypeDef RCC_OscInitStruct;