diff --git a/src/devices/machine/i82439hx.cpp b/src/devices/machine/i82439hx.cpp
index 2157bdc0043..86ac53874b7 100644
--- a/src/devices/machine/i82439hx.cpp
+++ b/src/devices/machine/i82439hx.cpp
@@ -78,6 +78,7 @@ void i82439hx_host_device::device_reset()
 	errcmd = 0x00;
 	errsts = 0x00;
 	errsyn = 0x00;
+	smiact_n = 1;
 }
 
 void i82439hx_host_device::map_extra(uint64_t memory_window_start, uint64_t memory_window_end, uint64_t memory_offset, address_space *memory_space,
@@ -85,14 +86,23 @@ void i82439hx_host_device::map_extra(uint64_t memory_window_start, uint64_t memo
 {
 	io_space->install_device(0, 0xffff, *static_cast<pci_host_device *>(this), &pci_host_device::io_configuration_access_map);
 
+	// memory hole at 512-640 kbytes
 	if((dramc & 0xc0) == 0x40)
 		memory_space->install_ram      (0x00000000, 0x0007ffff, &ram[0x00000000/4]);
 	else
 		memory_space->install_ram      (0x00000000, 0x0009ffff, &ram[0x00000000/4]);
 
-	if(smram & 0x40)
-		memory_space->install_ram      (0x000a0000, 0x000bffff, &ram[0x000a0000/4]);
+	// assume that map_extra of the northbridge is called after the video card has mepped its memory here
+	if (smram & 0x08)
+	{
+		if (smiact_n == 0)
+			memory_space->install_ram(0x000a0000, 0x000bffff, &ram[0x000a0000 / 4]);
+		else
+			if (smram & 0x40)
+				memory_space->install_ram(0x000a0000, 0x000bffff, &ram[0x000a0000 / 4]);
+	}
 
+	// assume that map_extra of the northbridge is called after the one of the southbridge
 	if(pam[1] & 0x01)
 		memory_space->install_rom      (0x000c0000, 0x000c3fff, &ram[0x000c0000/4]);
 	if(pam[1] & 0x02)
@@ -147,6 +157,7 @@ void i82439hx_host_device::map_extra(uint64_t memory_window_start, uint64_t memo
 		memory_space->install_writeonly(0x000f0000, 0x000fffff, &ram[0x000f0000/4]);
 
 	memory_space->install_ram          (0x00100000, 0x00efffff, &ram[0x00100000/4]);
+	// memory hole at 15-16 mbytes
 	if((dramc & 0xc0) != 0x80)
 		memory_space->install_ram      (0x00f00000, 0x00ffffff, &ram[0x00f00000/4]);
 
@@ -293,3 +304,14 @@ READ8_MEMBER (i82439hx_host_device::errsyn_r)
 {
 	return errsyn;
 }
+
+WRITE_LINE_MEMBER(i82439hx_host_device::smi_act_w)
+{
+	// state is 0 when smm is not active
+	// but smiact_n reflects the state of the SMIACT# pin
+	if (state == 0)
+		smiact_n = 1;
+	else
+		smiact_n = 0;
+	remap_cb();
+}
diff --git a/src/devices/machine/i82439hx.h b/src/devices/machine/i82439hx.h
index 0a4f47a5827..bab7dc20052 100644
--- a/src/devices/machine/i82439hx.h
+++ b/src/devices/machine/i82439hx.h
@@ -21,6 +21,8 @@ public:
 	void set_cpu_tag(const char *tag);
 	void set_ram_size(int ram_size);
 
+	DECLARE_WRITE_LINE_MEMBER(smi_act_w);
+
 protected:
 	virtual void device_start() override;
 	virtual void device_reset() override;
@@ -41,6 +43,7 @@ private:
 	uint8_t pcon, cc, dramec, dramc, dramt;
 	uint8_t pam[7], drb[8];
 	uint8_t drt, drat, smram, errcmd, errsts, errsyn;
+	int smiact_n;
 
 	DECLARE_READ8_MEMBER (pcon_r);
 	DECLARE_WRITE8_MEMBER(pcon_w);