diff --git a/hw/gt64xxx.c b/hw/gt64xxx.c
index 84e041fcfc..ccb6a7c1a2 100644
--- a/hw/gt64xxx.c
+++ b/hw/gt64xxx.c
@@ -229,9 +229,12 @@ static void gt64120_pci_mapping(GT64120State *s)
     target_phys_addr_t start, length;		   
 
     /* Update IO mapping */
-    start = s->regs[GT_PCI0IOLD] << 21;
-    length = ((s->regs[GT_PCI0IOHD] + 1) - (s->regs[GT_PCI0IOLD] & 0x7f)) << 21;
-    isa_mmio_init(start, length);
+    if ((s->regs[GT_PCI0IOLD] & 0x7f) <= s->regs[GT_PCI0IOHD])
+    {
+      start = s->regs[GT_PCI0IOLD] << 21;
+      length = ((s->regs[GT_PCI0IOHD] + 1) - (s->regs[GT_PCI0IOLD] & 0x7f)) << 21;
+      isa_mmio_init(start, length);
+    }
 }
 
 static void gt64120_writel (void *opaque, target_phys_addr_t addr,