diff --git a/src/gba/gba-io.c b/src/gba/gba-io.c
index 138390635..c4e4cec85 100644
--- a/src/gba/gba-io.c
+++ b/src/gba/gba-io.c
@@ -109,14 +109,6 @@ void GBAIOWrite(struct GBA* gba, uint32_t address, uint16_t value) {
 		case REG_IME:
 			GBAWriteIME(gba, value);
 			break;
-		case REG_HALTCNT:
-			value &= 0x80;
-			if (!value) {
-				GBAHalt(gba);
-			} else {
-				GBALog(GBA_LOG_STUB, "Stop unimplemented");
-			}
-			return;
 		default:
 			GBALog(GBA_LOG_STUB, "Stub I/O register write: %03x", address);
 			break;
@@ -125,6 +117,21 @@ void GBAIOWrite(struct GBA* gba, uint32_t address, uint16_t value) {
 	gba->memory.io[address >> 1] = value;
 }
 
+void GBAIOWrite8(struct GBA* gba, uint32_t address, uint8_t value) {
+	if (address == REG_HALTCNT) {
+		value &= 0x80;
+		if (!value) {
+			GBAHalt(gba);
+		} else {
+			GBALog(GBA_LOG_STUB, "Stop unimplemented");
+		}
+		return;
+	}
+	value <<= 8 * (address & 1);
+	value |= (gba->memory.io[(address & (SIZE_IO - 1)) >> 1]) & ~(0xFF << (8 * (address & 1)));
+	GBAIOWrite(gba, address, value);
+}
+
 void GBAIOWrite32(struct GBA* gba, uint32_t address, uint32_t value) {
 	switch (address) {
 	case REG_DMA0SAD_LO:
diff --git a/src/gba/gba-io.h b/src/gba/gba-io.h
index d0ff592b9..ab0463701 100644
--- a/src/gba/gba-io.h
+++ b/src/gba/gba-io.h
@@ -143,6 +143,7 @@ enum GBAIORegisters {
 
 void GBAIOInit(struct GBA* gba);
 void GBAIOWrite(struct GBA* gba, uint32_t address, uint16_t value);
+void GBAIOWrite8(struct GBA* gba, uint32_t address, uint8_t value);
 void GBAIOWrite32(struct GBA* gba, uint32_t address, uint32_t value);
 uint16_t GBAIORead(struct GBA* gba, uint32_t address);
 
diff --git a/src/gba/gba-memory.c b/src/gba/gba-memory.c
index 753decc81..cf2f1605f 100644
--- a/src/gba/gba-memory.c
+++ b/src/gba/gba-memory.c
@@ -385,6 +385,7 @@ void GBAStore8(struct ARMMemory* memory, uint32_t address, int8_t value, int* cy
 		((int8_t*) gbaMemory->iwram)[address & (SIZE_WORKING_IRAM - 1)] = value;
 		break;
 	case BASE_IO:
+		GBAIOWrite8(gbaMemory->p, address & (SIZE_IO - 1), value);
 		break;
 	case BASE_PALETTE_RAM:
 		break;