diff --git a/src/chipset/neat.c b/src/chipset/neat.c
index c1c2e827a..2990b5216 100644
--- a/src/chipset/neat.c
+++ b/src/chipset/neat.c
@@ -845,7 +845,7 @@ neat_write(uint16_t port, uint8_t val, void *priv)
                                  dev->ems_size);
                     }
 
-                    mem_a20_alt = val & RB12_GA20;
+                    mem_a20_key = !(val & RB12_GA20);
                     mem_a20_recalc();
                     break;