diff --git a/os/hal/ports/STM32/LLD/USBv1/hal_usb_lld.c b/os/hal/ports/STM32/LLD/USBv1/hal_usb_lld.c
index c8026ef44..7a9a096cb 100644
--- a/os/hal/ports/STM32/LLD/USBv1/hal_usb_lld.c
+++ b/os/hal/ports/STM32/LLD/USBv1/hal_usb_lld.c
@@ -143,7 +143,7 @@ static size_t usb_packet_read_to_buffer(usbep_t ep, uint8_t *buf) {
      in which the next received packet will be stored, so we need to
      read the counter of the OTHER buffer, which is where the last
      received packet was stored.*/
-  if (EPR_EP_TYPE_IS_ISO(epr) && !(epr & EPR_DTOG_RX))
+  if (EPR_EP_TYPE_IS_ISO(epr) && ((epr & EPR_DTOG_RX) != 0U))
     n = (size_t)udp->RXCOUNT1 & RXCOUNT_COUNT_MASK;
   else
     n = (size_t)udp->RXCOUNT0 & RXCOUNT_COUNT_MASK;
diff --git a/readme.txt b/readme.txt
index 6d1f4d092..eede19561 100644
--- a/readme.txt
+++ b/readme.txt
@@ -133,6 +133,8 @@
 - NEW: Added SPIv2 support also to STM32WB and STM32WL.
 - FIX: Re-opened and fixed bug #1100
        (backported to 20.3.5)(backported to 21.11.2).
+- FIX: Fixed wrong buffers toggling in STM32 USBv1 isochronous mode (bug #1232)
+       (backported to 20.3.5)(backported to 21.11.2).
 - FIX: Fixed STM32 RTCv2 registers synchronization errata (bug #1231)
        (backported to 20.3.5)(backported to 21.11.2).
 - FIX: Fixed STM32 ADCv1 and ADCv5 do not allow prescaler divide value of 1