diff --git a/arch/x86/kernel/cpu.c b/arch/x86/kernel/cpu.c
index e468ded5..c5857dea 100644
--- a/arch/x86/kernel/cpu.c
+++ b/arch/x86/kernel/cpu.c
@@ -824,7 +824,7 @@ void arch_show_extended_context(void)
 void arch_show_interrupt_context(const void *reg)
 {
 	const struct x86_regs *regs = reg;
-	int irqflags;
+	unsigned long irqflags;
 
 	irqflags = kprintf_lock();
 
diff --git a/kernel/debug.c b/kernel/debug.c
index 006a65bb..c2a1452e 100644
--- a/kernel/debug.c
+++ b/kernel/debug.c
@@ -45,12 +45,12 @@ void kputs(char *buf)
 
 #define KPRINTF_LOCAL_BUF_LEN 1024
 
-int kprintf_lock()
+unsigned long kprintf_lock(void)
 {
 	return ihk_mc_spinlock_lock(&kmsg_lock);
 }
 
-void kprintf_unlock(int irqflags)
+void kprintf_unlock(unsigned long irqflags)
 {
 	ihk_mc_spinlock_unlock(&kmsg_lock, irqflags);
 }
diff --git a/kernel/mem.c b/kernel/mem.c
index f5260062..a9401299 100644
--- a/kernel/mem.c
+++ b/kernel/mem.c
@@ -214,7 +214,7 @@ static void unhandled_page_fault(struct process *proc, void *fault_addr, void *r
 	struct process_vm *vm = proc->vm;
 	struct vm_range *range;
 	char found;
-	int irqflags;
+	unsigned long irqflags;
 	unsigned long error = ((struct x86_regs *)regs)->error;
 
 	irqflags = kprintf_lock();
diff --git a/lib/include/ihk/debug.h b/lib/include/ihk/debug.h
index e23a567f..f7c09b57 100644
--- a/lib/include/ihk/debug.h
+++ b/lib/include/ihk/debug.h
@@ -22,8 +22,8 @@ struct ihk_kmsg_buf {
 };
 
 extern int kprintf(const char *format, ...);
-extern int kprintf_lock();
-extern void kprintf_unlock(int irqflags);
+extern unsigned long kprintf_lock(void);
+extern void kprintf_unlock(unsigned long irqflags);
 extern int __kprintf(const char *format, ...);
 
 extern void panic(const char *msg);