diff --git a/arch/x86/core/intel64/cpu.c b/arch/x86/core/intel64/cpu.c
index 212d5c41ade..d078ff8a515 100644
--- a/arch/x86/core/intel64/cpu.c
+++ b/arch/x86/core/intel64/cpu.c
@@ -18,8 +18,6 @@
 
 __weak u8_t x86_cpu_loapics[] = { 0, 1, 2, 3 };
 
-extern FUNC_NORETURN void z_x86_prep_c(int dummy, struct multiboot_info *info);
-
 extern char x86_ap_start[];  /* AP entry point in locore.S */
 
 extern u8_t _exception_stack[];
diff --git a/arch/x86/include/kernel_arch_func.h b/arch/x86/include/kernel_arch_func.h
index 6299aa12be8..b3f2adeeb22 100644
--- a/arch/x86/include/kernel_arch_func.h
+++ b/arch/x86/include/kernel_arch_func.h
@@ -25,6 +25,10 @@ extern K_THREAD_STACK_DEFINE(_interrupt_stack1, CONFIG_ISR_STACK_SIZE);
 extern K_THREAD_STACK_DEFINE(_interrupt_stack2, CONFIG_ISR_STACK_SIZE);
 extern K_THREAD_STACK_DEFINE(_interrupt_stack3, CONFIG_ISR_STACK_SIZE);
 
+struct multiboot_info;
+
+extern FUNC_NORETURN void z_x86_prep_c(int dummy, struct multiboot_info *info);
+
 #endif
 
 #endif /* ZEPHYR_ARCH_X86_INCLUDE_KERNEL_ARCH_FUNC_H_ */