diff --git a/ports/samd/boards/ADAFRUIT_TRINKET_M0/mpconfigboard.h b/ports/samd/boards/ADAFRUIT_TRINKET_M0/mpconfigboard.h
index d3a6ba2d86..5732a20e3a 100644
--- a/ports/samd/boards/ADAFRUIT_TRINKET_M0/mpconfigboard.h
+++ b/ports/samd/boards/ADAFRUIT_TRINKET_M0/mpconfigboard.h
@@ -1,2 +1,4 @@
 #define MICROPY_HW_BOARD_NAME "Trinket M0"
 #define MICROPY_HW_MCU_NAME   "SAMD21E18A"
+
+#define MICROPY_HW_DFLL_USB_SYNC    (1)
diff --git a/ports/samd/boards/MINISAM_M4/mpconfigboard.h b/ports/samd/boards/MINISAM_M4/mpconfigboard.h
index 2dc403bad6..87acf301e3 100644
--- a/ports/samd/boards/MINISAM_M4/mpconfigboard.h
+++ b/ports/samd/boards/MINISAM_M4/mpconfigboard.h
@@ -1,4 +1,6 @@
 #define MICROPY_HW_BOARD_NAME "Mini SAM M4"
 #define MICROPY_HW_MCU_NAME   "SAMD51G19A"
 
+#define MICROPY_HW_DFLL_USB_SYNC    (1)
+
 #define MICROPY_HW_QSPIFLASH   GD25Q16C