diff --git a/kernel/include/kmalloc.h b/kernel/include/kmalloc.h
index 4574486b..d48704e1 100644
--- a/kernel/include/kmalloc.h
+++ b/kernel/include/kmalloc.h
@@ -34,7 +34,7 @@ void *__kmalloc(int size, ihk_mc_ap_flag flag);
 void __kfree(void *ptr);
 
 int _memcheck(void *ptr, char *msg, char *file, int line, int free);
-int memcheckall();
+int memcheckall(void);
 int freecheck(int runcount);
 void kmalloc_consolidate_free_list(void);
 
diff --git a/kernel/include/process.h b/kernel/include/process.h
index ec61c5b1..e76e2220 100644
--- a/kernel/include/process.h
+++ b/kernel/include/process.h
@@ -825,8 +825,8 @@ struct process *find_process(int pid, struct mcs_rwlock_node_irqsave *lock);
 void process_unlock(struct process *proc, struct mcs_rwlock_node_irqsave *lock);
 void chain_process(struct process *);
 void chain_thread(struct thread *);
-void proc_init();
-void set_timer();
+void proc_init(void);
+void set_timer(void);
 struct sig_pending *hassigpending(struct thread *thread);
 
 #endif
diff --git a/kernel/include/syscall.h b/kernel/include/syscall.h
index 35807168..b0764558 100644
--- a/kernel/include/syscall.h
+++ b/kernel/include/syscall.h
@@ -339,7 +339,7 @@ struct syscall_post {
 #define SYSCALL_FOOTER return do_syscall(&request, ihk_mc_get_processor_id(), 0)
 
 extern long do_syscall(struct syscall_request *req, int cpu, int pid);
-extern int obtain_clone_cpuid();
+int obtain_clone_cpuid(cpu_set_t *cpu_set);
 extern long syscall_generic_forwarding(int n, ihk_mc_user_context_t *ctx);
 
 #define DECLARATOR(number,name)		__NR_##name = number,
@@ -457,7 +457,7 @@ static inline unsigned long timespec_to_jiffy(const struct timespec *ats)
 	return ats->tv_sec * 100 + ats->tv_nsec / 10000000;
 }
 
-void reset_cputime();
+void reset_cputime(void);
 void set_cputime(int mode);
 int do_munmap(void *addr, size_t len);
 intptr_t do_mmap(intptr_t addr0, size_t len0, int prot, int flags, int fd,
diff --git a/lib/include/ihk/cpu.h b/lib/include/ihk/cpu.h
index 4e7792f7..5839f783 100644
--- a/lib/include/ihk/cpu.h
+++ b/lib/include/ihk/cpu.h
@@ -60,9 +60,9 @@ void ihk_mc_boot_cpu(int cpuid, unsigned long pc);
 int ihk_mc_get_processor_id(void);
 int ihk_mc_get_hardware_processor_id(void);
 int ihk_mc_get_numa_id(void);
-int ihk_mc_get_nr_cores();
-int ihk_mc_get_nr_linux_cores();
-int ihk_mc_get_osnum();
+int ihk_mc_get_nr_cores(void);
+int ihk_mc_get_nr_linux_cores(void);
+int ihk_mc_get_osnum(void);
 int ihk_mc_get_core(int id, unsigned long *linux_core_id, unsigned long *apic_id,
                     int *numa_id);
 int ihk_mc_get_ikc_cpu(int id);
@@ -78,7 +78,7 @@ void ihk_mc_init_context(ihk_mc_kernel_context_t *new_ctx,
                          void (*next_function)(void));
 
 int ihk_mc_get_extra_reg_id(unsigned long hw_config, unsigned long hw_config_ext);
-unsigned int ihk_mc_get_nr_extra_regs();
+unsigned int ihk_mc_get_nr_extra_regs(void);
 int ihk_mc_get_extra_reg_idx(int id);
 unsigned int ihk_mc_get_extra_reg_msr(int id);
 unsigned long ihk_mc_get_extra_reg_event(int id);
diff --git a/lib/include/ihk/mm.h b/lib/include/ihk/mm.h
index 3053de49..f9ff3715 100644
--- a/lib/include/ihk/mm.h
+++ b/lib/include/ihk/mm.h
@@ -224,7 +224,7 @@ void remote_flush_tlb_array_cpumask(struct process_vm *vm,
 		int cpu_id);
 
 int ihk_get_kmsg_buf(unsigned long *addr, unsigned long *size);
-char *ihk_get_kargs();
+char *ihk_get_kargs(void);
 
 int ihk_set_monitor(unsigned long addr, unsigned long size);
 int ihk_set_rusage(unsigned long addr, unsigned long size);