diff --git a/src/mess/machine/at.c b/src/mess/machine/at.c
index afede1354c0..3b370b023dc 100644
--- a/src/mess/machine/at.c
+++ b/src/mess/machine/at.c
@@ -272,7 +272,7 @@ void at_state::init_at_common()
 	/* MESS managed RAM */
 	membank("bank10")->set_base(m_ram->pointer());
 
-	if (m_ram->size() > 0x0a0000)
+	if (m_ram->size() > 0x100000)
 	{
 		offs_t ram_limit = 0x100000 + m_ram->size() - 0x100000;
 		space.install_read_bank(0x100000,  ram_limit - 1, "bank1");