diff --git a/hw/ppc/mac_newworld.c b/hw/ppc/mac_newworld.c
index d8e4db3b6a9ee4edd01a8b5fddcbee82a87e2caa..c6889d10550cbee5dcd56cc7c3950e172fb132cd 100644
--- a/hw/ppc/mac_newworld.c
+++ b/hw/ppc/mac_newworld.c
@@ -449,6 +449,8 @@ static void ppc_core99_init(QEMUMachineInitArgs *args)
     } else {
         fw_cfg_add_i32(fw_cfg, FW_CFG_PPC_TBFREQ, get_ticks_per_sec());
     }
+    /* Mac OS X requires a "known good" clock-frequency value; pass it one. */
+    fw_cfg_add_i32(fw_cfg, FW_CFG_PPC_CLOCKFREQ, 266000000);
 
     qemu_register_boot_set(fw_cfg_boot_set, fw_cfg);
 }
diff --git a/hw/ppc/mac_oldworld.c b/hw/ppc/mac_oldworld.c
index 3acca94432dfae316c98c9283bf8bfb565c1e071..8faff300ff48e82affb7f61cbdc7db4a0684af1f 100644
--- a/hw/ppc/mac_oldworld.c
+++ b/hw/ppc/mac_oldworld.c
@@ -333,6 +333,8 @@ static void ppc_heathrow_init(QEMUMachineInitArgs *args)
     } else {
         fw_cfg_add_i32(fw_cfg, FW_CFG_PPC_TBFREQ, get_ticks_per_sec());
     }
+    /* Mac OS X requires a "known good" clock-frequency value; pass it one. */
+    fw_cfg_add_i32(fw_cfg, FW_CFG_PPC_CLOCKFREQ, 266000000);
 
     qemu_register_boot_set(fw_cfg_boot_set, fw_cfg);
 }
diff --git a/include/hw/ppc/ppc.h b/include/hw/ppc/ppc.h
index acaf0d658027e7e60355eaa985148670443d6719..dfcad259b27b01db75a5c0704001f94744be4369 100644
--- a/include/hw/ppc/ppc.h
+++ b/include/hw/ppc/ppc.h
@@ -87,6 +87,7 @@ enum {
 #define FW_CFG_PPC_HEIGHT	(FW_CFG_ARCH_LOCAL + 0x01)
 #define FW_CFG_PPC_DEPTH	(FW_CFG_ARCH_LOCAL + 0x02)
 #define FW_CFG_PPC_TBFREQ	(FW_CFG_ARCH_LOCAL + 0x03)
+#define FW_CFG_PPC_CLOCKFREQ	(FW_CFG_ARCH_LOCAL + 0x04)
 #define FW_CFG_PPC_IS_KVM       (FW_CFG_ARCH_LOCAL + 0x05)
 #define FW_CFG_PPC_KVM_HC       (FW_CFG_ARCH_LOCAL + 0x06)
 #define FW_CFG_PPC_KVM_PID      (FW_CFG_ARCH_LOCAL + 0x07)