diff --git a/src/portable/microchip/samd21/dcd_samd21.c b/src/portable/microchip/samd21/dcd_samd21.c
index 0865f2bd..be1f4495 100644
--- a/src/portable/microchip/samd21/dcd_samd21.c
+++ b/src/portable/microchip/samd21/dcd_samd21.c
@@ -127,7 +127,7 @@ void dcd_set_config (uint8_t rhport, uint8_t config_num)
 uint32_t dcd_get_microframe(uint8_t rhport)
 {
   (void) rhport;
-  return USB->DEVICE.FNUM & (TU_BIT(14) - 1);
+  return USB->DEVICE.FNUM.reg & (TU_BIT(14) - 1);
 }
 
 /*------------------------------------------------------------------*/
diff --git a/src/portable/microchip/samd51/dcd_samd51.c b/src/portable/microchip/samd51/dcd_samd51.c
index fc3d31de..3dd6c88d 100644
--- a/src/portable/microchip/samd51/dcd_samd51.c
+++ b/src/portable/microchip/samd51/dcd_samd51.c
@@ -132,7 +132,7 @@ void dcd_set_config (uint8_t rhport, uint8_t config_num)
 uint32_t dcd_get_microframe(uint8_t rhport)
 {
   (void) rhport;
-  return USB->DEVICE.FNUM & (TU_BIT(14) - 1);
+  return USB->DEVICE.FNUM.reg & (TU_BIT(14) - 1);
 }
 
 /*------------------------------------------------------------------*/