diff --git a/src/boards/411.c b/src/boards/411.c
index bffad5d4..8f63948c 100644
--- a/src/boards/411.c
+++ b/src/boards/411.c
@@ -31,7 +31,7 @@
 #include "mapinc.h"
 #include "mmc3.h"
 
-uint8 submapper;
+static uint8 submapper;
 
 static void M411CW(uint32 A, uint8 V) {
 	int chrAND, chrOR;
diff --git a/src/boards/432.c b/src/boards/432.c
index 5687ea9e..e006fc96 100644
--- a/src/boards/432.c
+++ b/src/boards/432.c
@@ -23,7 +23,7 @@
 #include "mapinc.h"
 #include "mmc3.h"
 
-uint8 submapper;
+static uint8 submapper;
 
 static void M432CW(uint32 A, uint8 V) {
 	int chrAND = (EXPREGS[1] & 0x04) ? 0x7F : 0xFF;