diff --git a/ports/stm/common-hal/microcontroller/__init__.c b/ports/stm/common-hal/microcontroller/__init__.c
index b20f49e590..a2d8e02c3a 100644
--- a/ports/stm/common-hal/microcontroller/__init__.c
+++ b/ports/stm/common-hal/microcontroller/__init__.c
@@ -42,9 +42,12 @@
 #include "stm32f4xx_hal.h"
 
 void common_hal_mcu_delay_us(uint32_t delay) {
-    if (__get_PRIMASK() == 0x00000000) {
-    } else {
-    }
+    uint32_t ticks_per_us = HAL_RCC_GetSysClockFreq()/1000000;
+    delay *= ticks_per_us;
+    SysTick->LOAD = delay;
+    SysTick->CTRL = SysTick_CTRL_CLKSOURCE_Msk | SysTick_CTRL_ENABLE_Msk;
+    while ((SysTick->CTRL & SysTick_CTRL_COUNTFLAG_Msk) == 0) {}
+    SysTick->CTRL = 0;
 }
 
 volatile uint32_t nesting_count = 0;
diff --git a/ports/stm/stm32f4xx_hal_conf.h b/ports/stm/stm32f4xx_hal_conf.h
index 4c19f8561f..0a8d272d2a 100644
--- a/ports/stm/stm32f4xx_hal_conf.h
+++ b/ports/stm/stm32f4xx_hal_conf.h
@@ -122,7 +122,7 @@
   * @brief External Low Speed oscillator (LSE) value.
   */
 #if !defined  (LSE_VALUE)
- #define LSE_VALUE  ((uint32_t)32768U)    /*!< Value of the External Low Speed oscillator in Hz */
+ #define LSE_VALUE  32768    /*!< Value of the External Low Speed oscillator in Hz */
 #endif /* LSE_VALUE */
 
 #if !defined  (LSE_STARTUP_TIMEOUT)