diff --git a/os/hal/include/pwm.h b/os/hal/include/pwm.h
index e943df382..cdd1f43ca 100644
--- a/os/hal/include/pwm.h
+++ b/os/hal/include/pwm.h
@@ -118,8 +118,8 @@ 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 e7afb49cb..8901f4aa7 100644
--- a/readme.txt
+++ b/readme.txt
@@ -89,6 +89,8 @@
 *****************************************************************************
 
 *** 2.7.0 ***
+- FIX: Fixed invalid cast in PWM_FRACTION_TO_WIDTH() macro (bug #487)
+  (backported to 2.4.6 and 2.6.4).
 - FIX: Fixed wrong STM32 TIM9 clock source in PWM and ICU drivers (bug #486)
   (backported to 2.6.4).
 - FIX: Fixed MMC_SPI driver block_addresses is not initialized after