diff --git a/ports/mimxrt/Makefile b/ports/mimxrt/Makefile
index 7f93a6826d..ed7cc0630a 100644
--- a/ports/mimxrt/Makefile
+++ b/ports/mimxrt/Makefile
@@ -373,6 +373,10 @@ else
 CFLAGS += -Os -DNDEBUG
 endif
 
+# Set default values for optional variables
+MICROPY_HW_SDRAM_AVAIL ?= 0
+MICROPY_HW_SDRAM_SIZE ?= 0
+
 # Configure default compiler flags
 CFLAGS += \
 	$(INC) \
@@ -389,6 +393,8 @@ CFLAGS += \
 	-DFSL_SDK_ENABLE_DRIVER_CACHE_CONTROL=1 \
 	-DI2C_RETRY_TIMES=1000000 \
 	-DMICROPY_HW_FLASH_SIZE=$(MICROPY_HW_FLASH_SIZE) \
+	-DMICROPY_HW_SDRAM_AVAIL=$(MICROPY_HW_SDRAM_AVAIL) \
+	-DMICROPY_HW_SDRAM_SIZE=$(MICROPY_HW_SDRAM_SIZE) \
 	-DSPI_RETRY_TIMES=1000000 \
 	-DUART_RETRY_TIMES=1000000 \
 	-DXIP_BOOT_HEADER_ENABLE=1 \
@@ -458,12 +464,6 @@ CFLAGS += \
 	-DMBEDTLS_CONFIG_FILE='"mbedtls/mbedtls_config.h"'
 endif
 
-ifdef MICROPY_HW_SDRAM_AVAIL
-CFLAGS += \
-	-DMICROPY_HW_SDRAM_AVAIL=$(MICROPY_HW_SDRAM_AVAIL) \
-	-DMICROPY_HW_SDRAM_SIZE=$(MICROPY_HW_SDRAM_SIZE)
-endif
-
 CFLAGS += $(CFLAGS_MOD) $(CFLAGS_EXTRA)
 
 # =============================================================================
diff --git a/ports/mimxrt/board_init.c b/ports/mimxrt/board_init.c
index c3dbb652bc..12496890ac 100644
--- a/ports/mimxrt/board_init.c
+++ b/ports/mimxrt/board_init.c
@@ -52,7 +52,7 @@ void board_init(void) {
     CLOCK_EnableClock(kCLOCK_Iomuxc);
 
     // ------------- SDRAM ------------ //
-    #ifdef MICROPY_HW_SDRAM_AVAIL
+    #if MICROPY_HW_SDRAM_AVAIL
     mimxrt_sdram_init();
     #endif
 
diff --git a/ports/mimxrt/boards/MIMXRT1021.ld b/ports/mimxrt/boards/MIMXRT1021.ld
index 1263cd336c..60557f1bbf 100644
--- a/ports/mimxrt/boards/MIMXRT1021.ld
+++ b/ports/mimxrt/boards/MIMXRT1021.ld
@@ -27,7 +27,7 @@ dtcm_size           = 0x00018000;
 ocrm_start          = 0x20200000;
 ocrm_size           = 0x00018000;
 
-#ifdef MICROPY_HW_SDRAM_AVAIL
+#if MICROPY_HW_SDRAM_AVAIL
 sdram_start         = 0x80000000;
 sdram_size          = MICROPY_HW_SDRAM_SIZE;
 #endif
@@ -37,7 +37,7 @@ __stack_size__ = 0x6000;
 _estack = __StackTop;
 _sstack = __StackLimit;
 
-#ifdef MICROPY_HW_SDRAM_AVAIL
+#if MICROPY_HW_SDRAM_AVAIL
 _gc_heap_start = ORIGIN(m_sdram);
 _gc_heap_end = ORIGIN(m_sdram) + LENGTH(m_sdram);
 #else
diff --git a/ports/mimxrt/boards/MIMXRT1052.ld b/ports/mimxrt/boards/MIMXRT1052.ld
index f7c60d24f4..3e5739acf5 100644
--- a/ports/mimxrt/boards/MIMXRT1052.ld
+++ b/ports/mimxrt/boards/MIMXRT1052.ld
@@ -29,7 +29,7 @@ dtcm_size           = 0x00020000;
 ocrm_start          = 0x20200000;
 ocrm_size           = 0x00040000;
 
-#ifdef MICROPY_HW_SDRAM_AVAIL
+#if MICROPY_HW_SDRAM_AVAIL
 sdram_start         = 0x80000000;
 sdram_size          = MICROPY_HW_SDRAM_SIZE;
 #endif
@@ -39,7 +39,7 @@ __stack_size__ = 0x6000;
 _estack = __StackTop;
 _sstack = __StackLimit;
 
-#ifdef MICROPY_HW_SDRAM_AVAIL
+#if MICROPY_HW_SDRAM_AVAIL
 _gc_heap_start = ORIGIN(m_sdram);
 _gc_heap_end = ORIGIN(m_sdram) + LENGTH(m_sdram);
 #else
diff --git a/ports/mimxrt/boards/MIMXRT1062.ld b/ports/mimxrt/boards/MIMXRT1062.ld
index f588e5bd9e..fc4eb20c07 100644
--- a/ports/mimxrt/boards/MIMXRT1062.ld
+++ b/ports/mimxrt/boards/MIMXRT1062.ld
@@ -29,7 +29,7 @@ dtcm_size           = 0x00020000;
 ocrm_start          = 0x20200000;
 ocrm_size           = 0x000C0000;
 
-#ifdef MICROPY_HW_SDRAM_AVAIL
+#if MICROPY_HW_SDRAM_AVAIL
 sdram_start         = 0x80000000;
 sdram_size          = MICROPY_HW_SDRAM_SIZE;
 #endif
@@ -39,7 +39,7 @@ __stack_size__ = 0x8000;
 _estack = __StackTop;
 _sstack = __StackLimit;
 
-#ifdef MICROPY_HW_SDRAM_AVAIL
+#if MICROPY_HW_SDRAM_AVAIL
 _gc_heap_start = ORIGIN(m_sdram);
 _gc_heap_end = ORIGIN(m_sdram) + LENGTH(m_sdram);
 #else
diff --git a/ports/mimxrt/boards/MIMXRT1064.ld b/ports/mimxrt/boards/MIMXRT1064.ld
index b36c528453..148f1f23e2 100644
--- a/ports/mimxrt/boards/MIMXRT1064.ld
+++ b/ports/mimxrt/boards/MIMXRT1064.ld
@@ -31,7 +31,7 @@ dtcm_size           = 0x00020000;
 ocrm_start          = 0x20200000;
 ocrm_size           = 0x000C0000;
 
-#ifdef MICROPY_HW_SDRAM_AVAIL
+#if MICROPY_HW_SDRAM_AVAIL
 sdram_start         = 0x80000000;
 sdram_size          = MICROPY_HW_SDRAM_SIZE;
 #endif
@@ -41,7 +41,7 @@ __stack_size__ = 0x6000;
 _estack = __StackTop;
 _sstack = __StackLimit;
 
-#ifdef MICROPY_HW_SDRAM_AVAIL
+#if MICROPY_HW_SDRAM_AVAIL
 _gc_heap_start = ORIGIN(m_sdram);
 _gc_heap_end = ORIGIN(m_sdram) + LENGTH(m_sdram);
 #else
diff --git a/ports/mimxrt/boards/common.ld b/ports/mimxrt/boards/common.ld
index 7aee66e2e8..fbc99da3dd 100644
--- a/ports/mimxrt/boards/common.ld
+++ b/ports/mimxrt/boards/common.ld
@@ -46,7 +46,7 @@ MEMORY
   m_dtcm         (RW) : ORIGIN = dtcm_start,            LENGTH = dtcm_size
   m_ocrm         (RW) : ORIGIN = ocrm_start,            LENGTH = ocrm_size
 
-  #ifdef MICROPY_HW_SDRAM_AVAIL
+  #if MICROPY_HW_SDRAM_AVAIL
   m_sdram        (RX) : ORIGIN = sdram_start,           LENGTH = sdram_size
   #endif
 }
@@ -55,7 +55,7 @@ MEMORY
 SECTIONS
 {
   __flash_start = flash_start;
-  #ifdef MICROPY_HW_SDRAM_AVAIL
+  #if MICROPY_HW_SDRAM_AVAIL
   __sdram_start = sdram_start;
   #endif
   __vfs_start = ORIGIN(m_vfs);