diff --git a/src/mess/drivers/gb.c b/src/mess/drivers/gb.c
index 38e3f74ac41..d894ad8cd6c 100644
--- a/src/mess/drivers/gb.c
+++ b/src/mess/drivers/gb.c
@@ -485,7 +485,7 @@ READ8_MEMBER(gb_state::gb_cart_r)
 	{
 		if (offset < 0x100)
 		{
-			UINT8 *ROM = space.machine().root_device().memregion("maincpu")->base();
+			UINT8 *ROM = m_region_maincpu->base();
 			return ROM[offset];
 		}
 		else if (m_cartslot->m_cart)
@@ -505,12 +505,12 @@ READ8_MEMBER(gb_state::gbc_cart_r)
 	{
 		if (offset < 0x100)
 		{
-			UINT8 *ROM = space.machine().root_device().memregion("maincpu")->base();
+			UINT8 *ROM = m_region_maincpu->base();
 			return ROM[offset];
 		}
 		else if (offset >= 0x200 && offset < 0x900)
 		{
-			UINT8 *ROM = space.machine().root_device().memregion("maincpu")->base();
+			UINT8 *ROM = m_region_maincpu->base();
 			return ROM[offset - 0x100];
 		}
 		else if (m_cartslot->m_cart)
diff --git a/src/mess/includes/gb.h b/src/mess/includes/gb.h
index aa373b76ddf..185ba6c486a 100644
--- a/src/mess/includes/gb.h
+++ b/src/mess/includes/gb.h
@@ -113,6 +113,7 @@ public:
 		: driver_device(mconfig, type, tag)
 		, m_cartslot(*this, "gbslot")
 		, m_maincpu(*this, "maincpu")
+		, m_region_maincpu(*this, "maincpu")
 		, m_rambank(*this, "cgb_ram")
 		, m_inputs(*this, "INPUTS")
 	{ }
@@ -207,6 +208,7 @@ public:
 
 protected:
 	required_device<lr35902_cpu_device> m_maincpu;
+	required_memory_region m_region_maincpu;
 	optional_memory_bank m_rambank;   // cgb
 	required_ioport m_inputs;