diff --git a/ports/nrf/Makefile b/ports/nrf/Makefile
index 25076020d4..cffbbefe1b 100644
--- a/ports/nrf/Makefile
+++ b/ports/nrf/Makefile
@@ -206,8 +206,10 @@ SRC_C += \
 	device/$(MCU_VARIANT)/system_$(MCU_SUB_VARIANT).c \
 	device/$(MCU_VARIANT)/startup_$(MCU_SUB_VARIANT).c \
 
+ifneq ($(FROZEN_MPY_DIR),)
 FROZEN_MPY_PY_FILES := $(shell find -L $(FROZEN_MPY_DIR) -type f -name '*.py')
 FROZEN_MPY_MPY_FILES := $(addprefix $(BUILD)/,$(FROZEN_MPY_PY_FILES:.py=.mpy))
+endif
 
 OBJ += $(PY_O) $(addprefix $(BUILD)/, $(SRC_C:.c=.o))
 OBJ += $(addprefix $(BUILD)/, $(SRC_LIB:.c=.o))