diff --git a/src/northbridge/amd/agesa/family15tn/northbridge.c b/src/northbridge/amd/agesa/family15tn/northbridge.c
index dc68f77e94..f91f69098b 100644
--- a/src/northbridge/amd/agesa/family15tn/northbridge.c
+++ b/src/northbridge/amd/agesa/family15tn/northbridge.c
@@ -811,8 +811,9 @@ static void domain_set_resources(device_t dev)
 				sizek = 0;
 			}
 			else {
+				uint64_t topmem2 = bsp_topmem2();
 				basek = 4*1024*1024;
-				sizek -= (4*1024*1024 - mmio_basek);
+				sizek = topmem2/1024 - basek;
 			}
 		}