diff --git a/src/sio/sio_vt82c686.c b/src/sio/sio_vt82c686.c
index 192865c5a..235dfbd32 100644
--- a/src/sio/sio_vt82c686.c
+++ b/src/sio/sio_vt82c686.c
@@ -103,20 +103,24 @@ vt82c686_write(uint16_t port, uint8_t val, void *priv)
     if (!dev->config_enable)
 	return;
 
+    /* NOTE: Registers are [0xE0:0xFF] but we store them as [0x00:0x1F]. */
     if (!(port & 1)) {
-	/* Registers start at 0xE0 but we cut them down to start at 0x00. */
-	dev->cur_reg = (val & 0x1f);
+	dev->cur_reg = val;
 	return;
     }
 
+    if (dev->cur_reg < 0xe0)
+    	return;
+    uint8_t reg = dev->cur_reg & 0x1f;
+
     /* Read-only registers */
-    if ((dev->cur_reg < 0x02) || (dev->cur_reg == 0x04) || (dev->cur_reg == 0x05) || ((dev->cur_reg >= 0x09) && (dev->cur_reg < 0x0e)) ||
-	(dev->cur_reg == 0x13) || (dev->cur_reg == 0x15) || (dev->cur_reg == 0x17) || (dev->cur_reg >= 0x19))
+    if ((reg < 0x02) || (reg == 0x04) || (reg == 0x05) || ((reg >= 0x09) && (reg < 0x0e)) ||
+	(reg == 0x13) || (reg == 0x15) || (reg == 0x17) || (reg >= 0x19))
 	return;
 
-    switch (dev->cur_reg) {
+    switch (reg) {
 	case 0x02:
-		dev->regs[dev->cur_reg] = val;
+		dev->regs[reg] = val;
 		vt82c686_lpt_handler(dev);
 		vt82c686_serial_handler(dev, 0);
 		vt82c686_serial_handler(dev, 1);
@@ -124,27 +128,27 @@ vt82c686_write(uint16_t port, uint8_t val, void *priv)
 		break;
 
 	case 0x03:
-		dev->regs[dev->cur_reg] = val;
+		dev->regs[reg] = val;
 		vt82c686_fdc_handler(dev);
 		break;
 
 	case 0x06:
-		dev->regs[dev->cur_reg] = val;
+		dev->regs[reg] = val;
 		vt82c686_lpt_handler(dev);
 		break;
 
 	case 0x07:
-		dev->regs[dev->cur_reg] = val;
+		dev->regs[reg] = val;
 		vt82c686_serial_handler(dev, 0);
 		break;
 
 	case 0x08:
-		dev->regs[dev->cur_reg] = val;
+		dev->regs[reg] = val;
 		vt82c686_serial_handler(dev, 1);
 		break;
 
 	default:
-		dev->regs[dev->cur_reg] = val;
+		dev->regs[reg] = val;
 		break;
     }
 }
@@ -156,10 +160,13 @@ vt82c686_read(uint16_t port, void *priv)
     vt82c686_t *dev = (vt82c686_t *) priv;
     uint8_t ret = 0xff;
     
+    /* NOTE: Registers are [0xE0:0xFF] but we store them as [0x00:0x1F]. */
     if (!(port & 1))
-	ret = dev->cur_reg | 0xe0;
+	ret = dev->cur_reg;
+    else if (dev->cur_reg < 0xe0)
+	ret = 0xff;
     else
-	ret = dev->regs[dev->cur_reg];
+	ret = dev->regs[dev->cur_reg & 0x1f];
 
     return ret;
 }