diff --git a/os/hal/include/pwm.h b/os/hal/include/pwm.h
index df155f63e..d50da54c4 100644
--- a/os/hal/include/pwm.h
+++ b/os/hal/include/pwm.h
@@ -125,8 +125,8 @@ typedef void (*pwmcallback_t)(PWMDriver *pwmp);
  * @api
  */
 #define PWM_FRACTION_TO_WIDTH(pwmp, denominator, numerator)                 \
-  ((uint16_t)((((uint32_t)(pwmp)->period) *                                 \
-               (uint32_t)(numerator)) / (uint32_t)(denominator)))
+  ((pwmcnt_t)((((pwmcnt_t)(pwmp)->period) *                                 \
+               (pwmcnt_t)(numerator)) / (pwmcnt_t)(denominator)))
 
 /**
  * @brief   Converts from degrees to pulse width.
diff --git a/readme.txt b/readme.txt
index 712ad5f9c..0bf9e8c1a 100644
--- a/readme.txt
+++ b/readme.txt
@@ -79,6 +79,7 @@
 *****************************************************************************
 
 *** 2.4.6 ***
+- FIX: Fixed invalid cast in PWM_FRACTION_TO_WIDTH() macro (bug #487).
 - FIX: Fixed spurious callback in ICU driver (bug #461).
 - FIX: Fixed wrong vector names for STM32Lxx.
 - FIX: Fixed wrong MCO2 check in STM32F4xx HAL driver (bug #447).