diff --git a/include/mgba/internal/gb/io.h b/include/mgba/internal/gb/io.h
index 92917d70a..169199230 100644
--- a/include/mgba/internal/gb/io.h
+++ b/include/mgba/internal/gb/io.h
@@ -87,6 +87,7 @@ enum GBIORegisters {
 	REG_KEY0 = 0x4C,
 	REG_KEY1 = 0x4D,
 	REG_VBK = 0x4F,
+	REG_BANK = 0x50,
 	REG_HDMA1 = 0x51,
 	REG_HDMA2 = 0x52,
 	REG_HDMA3 = 0x53,
diff --git a/src/gb/io.c b/src/gb/io.c
index ea9eb7b2e..280ca1ddf 100644
--- a/src/gb/io.c
+++ b/src/gb/io.c
@@ -56,6 +56,7 @@ MGBA_EXPORT const char* const GBIORegisterNames[] = {
 	[REG_KEY0] = "KEY0",
 	[REG_KEY1] = "KEY1",
 	[REG_VBK] = "VBK",
+	[REG_BANK] = "BANK",
 	[REG_HDMA1] = "HDMA1",
 	[REG_HDMA2] = "HDMA2",
 	[REG_HDMA3] = "HDMA3",
@@ -185,10 +186,10 @@ void GBIOReset(struct GB* gb) {
 	GBIOWrite(gb, REG_NR51, 0xF3);
 	if (!gb->biosVf) {
 		GBIOWrite(gb, REG_LCDC, 0x91);
-		gb->memory.io[0x50] = 1;
+		gb->memory.io[REG_BANK] = 1;
 	} else {
 		GBIOWrite(gb, REG_LCDC, 0x00);
-		gb->memory.io[0x50] = 0xFF;
+		gb->memory.io[REG_BANK] = 0xFF;
 	}
 	GBIOWrite(gb, REG_SCY, 0x00);
 	GBIOWrite(gb, REG_SCX, 0x00);
@@ -459,8 +460,8 @@ void GBIOWrite(struct GB* gb, unsigned address, uint8_t value) {
 		GBVideoWriteSTAT(&gb->video, value);
 		value = gb->video.stat;
 		break;
-	case 0x50:
-		if (gb->memory.io[0x50] != 0xFF) {
+	case REG_BANK:
+		if (gb->memory.io[REG_BANK] != 0xFF) {
 			break;
 		}
 		GBUnmapBIOS(gb);
diff --git a/src/gb/serialize.c b/src/gb/serialize.c
index e6b053b9b..002b5a650 100644
--- a/src/gb/serialize.c
+++ b/src/gb/serialize.c
@@ -139,7 +139,7 @@ bool GBDeserialize(struct GB* gb, const struct GBSerializedState* state) {
 		mLOG(GB_STATE, WARN, "Savestate is corrupted: OCPS is out of range");
 	}
 	bool differentBios = !gb->biosVf || gb->model != state->model;
-	if (state->io[0x50] == 0xFF) {
+	if (state->io[REG_BANK] == 0xFF) {
 		if (differentBios) {
 			mLOG(GB_STATE, WARN, "Incompatible savestate, please restart with correct BIOS in %s mode", GBModelToName(state->model));
 			error = true;
@@ -206,7 +206,7 @@ bool GBDeserialize(struct GB* gb, const struct GBSerializedState* state) {
 	GBTimerDeserialize(&gb->timer, state);
 	GBAudioDeserialize(&gb->audio, state);
 
-	if (gb->memory.io[0x50] == 0xFF) {
+	if (gb->memory.io[REG_BANK] == 0xFF) {
 		GBMapBIOS(gb);
 	} else {
 		GBUnmapBIOS(gb);