diff --git a/ports/nrf/Makefile b/ports/nrf/Makefile
index 13a148df3b..d1745a70ef 100755
--- a/ports/nrf/Makefile
+++ b/ports/nrf/Makefile
@@ -73,11 +73,11 @@ INC += -I$(BUILD)
 INC += -I$(BUILD)/genhdr
 INC += -I./../../lib/cmsis/inc
 INC += -I./boards/$(BOARD)
-INC += -I./nrfx
-INC += -I./nrfx/hal
-INC += -I./nrfx/mdk
-INC += -I./nrfx/drivers/include
-INC += -I./nrfx/drivers/src
+INC += -isystem ./nrfx
+INC += -isystem ./nrfx/hal
+INC += -isystem ./nrfx/mdk
+INC += -isystem ./nrfx/drivers/include
+INC += -isystem ./nrfx/drivers/src
 INC += -I./bluetooth
 INC += -I./peripherals
 INC += -I../../lib/mp-readline
@@ -100,8 +100,8 @@ CFLAGS += $(OPTIMIZATION_FLAGS)
 CFLAGS += $(INC) -Wall -Werror -std=gnu11 -nostdlib -fshort-enums $(BASE_CFLAGS) $(CFLAGS_MOD) $(COPT)
 
 # Undo some warnings.
-# nrfx uses undefined preprocessor variables quite casually, so we can't do warning checks for these.
-CFLAGS += -Wno-undef
+## nrfx uses undefined preprocessor variables quite casually, so we can't do warning checks for these.
+#CFLAGS += -Wno-undef
 # nrfx does casts that increase alignment requirements.
 CFLAGS += -Wno-cast-align
 
@@ -240,6 +240,8 @@ endif
 OBJ += $(addprefix $(BUILD)/, $(SRC_S:.s=.o))
 OBJ += $(addprefix $(BUILD)/, $(SRC_MOD:.c=.o))
 
+$(addprefix $(BUILD)/, $(SRC_NRFX:.c=.o)): CFLAGS += -Wno-undef
+
 $(BUILD)/$(FATFS_DIR)/ff.o: COPT += -Os
 $(filter $(PY_BUILD)/../extmod/vfs_fat_%.o, $(PY_O)): COPT += -Os
 
diff --git a/ports/nrf/common-hal/busio/SPI.c b/ports/nrf/common-hal/busio/SPI.c
index f27f0e267b..fdfe61811b 100644
--- a/ports/nrf/common-hal/busio/SPI.c
+++ b/ports/nrf/common-hal/busio/SPI.c
@@ -34,6 +34,22 @@
 #include "nrfx_spim.h"
 #include "nrf_gpio.h"
 
+#ifndef NRFX_SPIM3_ENABLED
+#define NRFX_SPIM3_ENABLED (0)
+#endif
+
+#ifndef NRFX_SPIM2_ENABLED
+#define NRFX_SPIM2_ENABLED (0)
+#endif
+
+#ifndef NRFX_SPIM1_ENABLED
+#define NRFX_SPIM1_ENABLED (0)
+#endif
+
+#ifndef NRFX_SPIM0_ENABLED
+#define NRFX_SPIM0_ENABLED (0)
+#endif
+
 // These are in order from highest available frequency to lowest (32MHz first, then 8MHz).
 STATIC spim_peripheral_t spim_peripherals[] = {
 #if NRFX_CHECK(NRFX_SPIM3_ENABLED)
diff --git a/ports/nrf/supervisor/qspi_flash.c b/ports/nrf/supervisor/qspi_flash.c
index 5ab56c6bc4..7ca27d56c4 100644
--- a/ports/nrf/supervisor/qspi_flash.c
+++ b/ports/nrf/supervisor/qspi_flash.c
@@ -201,7 +201,7 @@ void spi_flash_init(void) {
         .irq_priority = 7,
     };
 
-#if EXTERNAL_FLASH_QSPI_DUAL
+#if defined(EXTERNAL_FLASH_QSPI_DUAL)
     qspi_cfg.pins.io1_pin = MICROPY_QSPI_DATA1;
     qspi_cfg.prot_if.readoc = NRF_QSPI_READOC_READ2O;
     qspi_cfg.prot_if.writeoc = NRF_QSPI_WRITEOC_PP2O;