diff --git a/kernel/syscall.c b/kernel/syscall.c
index 5b699eec..6ad36eeb 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -639,9 +639,6 @@ out:
 	return error;
 }
 
-#ifdef UNDEFINED
-mmap() {}
-#endif
 SYSCALL_DECLARE(mmap)
 {
 	const int supported_flags = 0
@@ -939,9 +936,6 @@ out2:
 	return (!error)? addr: error;
 }
 
-#ifdef UNDEFINED
-munmap() {}
-#endif
 SYSCALL_DECLARE(munmap)
 {
 	const uintptr_t addr = ihk_mc_syscall_arg0(ctx);
@@ -975,9 +969,6 @@ out:
 	return error;
 }
 
-#ifdef UNDEFINED
-mprotect() {}
-#endif
 SYSCALL_DECLARE(mprotect)
 {
 	const intptr_t start = ihk_mc_syscall_arg0(ctx);
@@ -1807,9 +1798,6 @@ SYSCALL_DECLARE(sigaltstack)
 	return 0;
 }
 
-#ifdef UNDEFINED
-madvise() {}
-#endif
 SYSCALL_DECLARE(madvise)
 {
 	const uintptr_t start = (uintptr_t)ihk_mc_syscall_arg0(ctx);
@@ -2200,9 +2188,6 @@ SYSCALL_DECLARE(sched_yield)
 	return -ENOSYS;
 }
 
-#ifdef UNDEFINED
-mlock() {}
-#endif
 SYSCALL_DECLARE(mlock)
 {
 	const uintptr_t start0 = ihk_mc_syscall_arg0(ctx);
@@ -2378,9 +2363,6 @@ out2:
 	return error;
 }
 
-#ifdef UNDEFINED
-munlock() {}
-#endif
 SYSCALL_DECLARE(munlock)
 {
 	const uintptr_t start0 = ihk_mc_syscall_arg0(ctx);
@@ -2534,9 +2516,6 @@ out2:
 	return error;
 }
 
-#ifdef UNDEFINED
-remap_file_pages() {}
-#endif
 SYSCALL_DECLARE(remap_file_pages)
 {
 	const uintptr_t start0 = ihk_mc_syscall_arg0(ctx);
@@ -2613,9 +2592,6 @@ out:
 	return error;
 }
 
-#ifdef UNDEFINED
-mremap() {}
-#endif
 SYSCALL_DECLARE(mremap)
 {
 	const uintptr_t oldaddr = ihk_mc_syscall_arg0(ctx);