diff --git a/hw/ppc_newworld.c b/hw/ppc_newworld.c
index a09f096ba32598296c38c7ae618192267e7fba3b..a4c714ae7f304028b0635402f857bf4d01a990b7 100644
--- a/hw/ppc_newworld.c
+++ b/hw/ppc_newworld.c
@@ -119,7 +119,11 @@ static void ppc_core99_init (ram_addr_t ram_size,
 
     /* init CPUs */
     if (cpu_model == NULL)
+#ifdef TARGET_PPC64
+        cpu_model = "970fx";
+#else
         cpu_model = "G4";
+#endif
     for (i = 0; i < smp_cpus; i++) {
         env = cpu_init(cpu_model);
         if (!env) {
@@ -385,6 +389,9 @@ static QEMUMachine core99_machine = {
     .desc = "Mac99 based PowerMAC",
     .init = ppc_core99_init,
     .max_cpus = MAX_CPUS,
+#ifdef TARGET_PPC64
+    .is_default = 1,
+#endif
 };
 
 static void core99_machine_init(void)
diff --git a/hw/ppc_oldworld.c b/hw/ppc_oldworld.c
index c90b1514870024cc99b12e587be4b611b2bb452e..7ccc6a14718c4e361d064a25e3ba3b44731c6c11 100644
--- a/hw/ppc_oldworld.c
+++ b/hw/ppc_oldworld.c
@@ -409,7 +409,9 @@ static QEMUMachine heathrow_machine = {
     .desc = "Heathrow based PowerMAC",
     .init = ppc_heathrow_init,
     .max_cpus = MAX_CPUS,
+#ifndef TARGET_PPC64
     .is_default = 1,
+#endif
 };
 
 static void heathrow_machine_init(void)