diff --git a/ports/atmel-samd/mpconfigport.mk b/ports/atmel-samd/mpconfigport.mk
index ed734ce679..032e49ce36 100644
--- a/ports/atmel-samd/mpconfigport.mk
+++ b/ports/atmel-samd/mpconfigport.mk
@@ -105,6 +105,7 @@ CIRCUITPY_FRAMEBUFFERIO ?= $(CIRCUITPY_FULL_BUILD)
 CIRCUITPY_PS2IO ?= 1
 CIRCUITPY_RGBMATRIX ?= $(CIRCUITPY_FRAMEBUFFERIO)
 CIRCUITPY_SAMD ?= 1
+CIRCUITPY_SYNTHIO_MAX_CHANNELS = 12
 CIRCUITPY_WATCHDOG ?= 1
 
 endif # samd51