diff --git a/kernels/litenes/src/mmc.c b/kernels/litenes/src/mmc.c
index 4fda05c..b60f2e7 100644
--- a/kernels/litenes/src/mmc.c
+++ b/kernels/litenes/src/mmc.c
@@ -2,6 +2,7 @@
 #include "ppu.h"
 #include <klib.h>
 
+byte mmc_id;
 #define MMC_MAX_PAGE_COUNT 1
 
 static byte mmc_chr_pages[MMC_MAX_PAGE_COUNT][0x2000];
diff --git a/kernels/litenes/src/mmc.h b/kernels/litenes/src/mmc.h
index 5ec8fae..3376ce1 100644
--- a/kernels/litenes/src/mmc.h
+++ b/kernels/litenes/src/mmc.h
@@ -1,8 +1,8 @@
 #include "common.h"
 
-byte mmc_id;
+extern byte mmc_id;
 
 byte mmc_read(word address);
 void mmc_write(word address, byte data);
 void mmc_copy(word address, byte *source, int length);
-void mmc_append_chr_rom_page(byte *source);
\ No newline at end of file
+void mmc_append_chr_rom_page(byte *source);