diff --git a/arch/x86_64/tools/mcreboot-smp-x86.sh.in b/arch/x86_64/tools/mcreboot-smp-x86.sh.in
index 0e87e049..dd8eeafe 100644
--- a/arch/x86_64/tools/mcreboot-smp-x86.sh.in
+++ b/arch/x86_64/tools/mcreboot-smp-x86.sh.in
@@ -46,8 +46,9 @@ turbo=""
 ihk_irq=""
 umask_old=`umask`
 idle_halt=""
+allow_oversubscribe=""
 
-while getopts :tk:c:m:o:f:r:q:i:d:e:h OPT
+while getopts :tk:c:m:o:f:r:q:i:d:e:hO OPT
 do
 	case ${OPT} in
 	f)	facility=${OPTARG}
@@ -74,6 +75,8 @@ do
 		;;
 	h) idle_halt="idle_halt"
 		;;
+	O) allow_oversubscribe="allow_oversubscribe"
+		;;
 	*)  echo "invalid option -${OPT}" >&2
 		exit 1
 	esac
@@ -419,7 +422,7 @@ if ! ${SBINDIR}/ihkosctl 0 load ${KERNDIR}/mckernel.img; then
 fi
 
 # Set kernel arguments
-if ! ${SBINDIR}/ihkosctl 0 kargs "hidos $turbo $idle_halt dump_level=${DUMP_LEVEL} $extra_kopts"; then
+if ! ${SBINDIR}/ihkosctl 0 kargs "hidos $turbo $idle_halt dump_level=${DUMP_LEVEL} $extra_kopts $allow_oversubscribe"; then
 	echo "error: setting kernel arguments" >&2
 	error_exit "os_created"
 fi
diff --git a/kernel/include/process.h b/kernel/include/process.h
index 8eb8142c..1bf8f275 100644
--- a/kernel/include/process.h
+++ b/kernel/include/process.h
@@ -278,6 +278,7 @@ struct resource_set {
 extern struct list_head	resource_set_list;
 extern mcs_rwlock_lock_t	resource_set_lock;
 extern int idle_halt;
+extern int allow_oversubscribe;
 
 struct process_hash {
 	struct list_head	list[HASH_SIZE];
diff --git a/kernel/init.c b/kernel/init.c
index 01c581e9..88d11682 100644
--- a/kernel/init.c
+++ b/kernel/init.c
@@ -150,6 +150,12 @@ static void parse_kargs(void)
 	if (ptr) {
 		idle_halt = 1;
 	}
+
+	/* allow_oversubscribe option */
+	ptr = find_command_line("allow_oversubscribe");
+	if (ptr) {
+		allow_oversubscribe = 1;
+	}
 }
 
 extern void ihk_mc_get_boot_time(unsigned long *tv_sec, unsigned long *tv_nsec);
diff --git a/kernel/process.c b/kernel/process.c
index 3a5da9f3..8d03bb2c 100644
--- a/kernel/process.c
+++ b/kernel/process.c
@@ -101,6 +101,7 @@ struct list_head resource_set_list;
 mcs_rwlock_lock_t    resource_set_lock;
 
 int idle_halt = 0;
+int allow_oversubscribe = 0;
 
 void
 init_process(struct process *proc, struct process *parent)
diff --git a/kernel/syscall.c b/kernel/syscall.c
index b8ea8142..d79d84e8 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -2343,6 +2343,7 @@ unsigned long do_fork(int clone_flags, unsigned long newsp,
 	struct syscall_request request1 IHK_DMA_ALIGN;
 	int ptrace_event = 0;
 	int termsig = clone_flags & 0x000000ff;
+	const struct ihk_mc_cpu_info *cpu_info = ihk_mc_get_cpu_info();
 
     dkprintf("do_fork,flags=%08x,newsp=%lx,ptidptr=%lx,ctidptr=%lx,tls=%lx,curpc=%lx,cursp=%lx",
             clone_flags, newsp, parent_tidptr, child_tidptr, tlsblock_base, curpc, cursp);
@@ -2382,6 +2383,11 @@ unsigned long do_fork(int clone_flags, unsigned long newsp,
 		return -EINVAL;
 	}
 
+	if (!allow_oversubscribe && rusage->num_threads >= cpu_info->ncpus) {
+		kprintf("%s: ERROR: CPU oversubscription is not allowed. Specify -O option in mcreboot.sh to allow it.\n", __FUNCTION__);
+        return -EINVAL;
+	}
+
 	cpuid = obtain_clone_cpuid(&old->cpu_set);
     if (cpuid == -1) {
 		kprintf("do_fork,core not available\n");