diff --git a/src/portable/synopsys/dwc2/dwc2_bcm.h b/src/portable/synopsys/dwc2/dwc2_bcm.h
index 0263d19ba..fcec0b0d2 100644
--- a/src/portable/synopsys/dwc2/dwc2_bcm.h
+++ b/src/portable/synopsys/dwc2/dwc2_bcm.h
@@ -47,7 +47,7 @@ static inline void dwc2_dcd_int_enable(uint8_t rhport)
 {
   (void) rhport;
   BP_EnableIRQ(USB_IRQn);
-  __asm__ volatile("isb");
+  __asm__ volatile("isb"); // needed if TIMER1 IRQ is not enabled !?
 }
 
 TU_ATTR_ALWAYS_INLINE
@@ -55,7 +55,7 @@ static inline void dwc2_dcd_int_disable (uint8_t rhport)
 {
   (void) rhport;
   BP_DisableIRQ(USB_IRQn);
-  __asm__ volatile("isb");
+  __asm__ volatile("isb"); // needed if TIMER1 IRQ is not enabled !?
 }
 
 static inline void dwc2_remote_wakeup_delay(void)