diff --git a/mrbgems/mruby-kernel-ext/src/kernel.c b/mrbgems/mruby-kernel-ext/src/kernel.c
index 3229c9c5c..4a18e5903 100644
--- a/mrbgems/mruby-kernel-ext/src/kernel.c
+++ b/mrbgems/mruby-kernel-ext/src/kernel.c
@@ -270,17 +270,17 @@ mrb_mruby_kernel_ext_gem_init(mrb_state *mrb)
 {
   struct RClass *krn = mrb->kernel_module;
 
-  mrb_define_module_function_id(mrb, krn, MRB_SYM(fail), mrb_f_raise, MRB_ARGS_OPT(2));
-  mrb_define_module_function_id(mrb, krn, MRB_SYM(caller), mrb_f_caller, MRB_ARGS_OPT(2));
-  mrb_define_method_id(mrb, krn, MRB_SYM(__method__), mrb_f_method, MRB_ARGS_NONE());
-  mrb_define_method_id(mrb, krn, MRB_SYM(__callee__), mrb_f_callee, MRB_ARGS_NONE());
-  mrb_define_module_function_id(mrb, krn, MRB_SYM(Integer), mrb_f_integer, MRB_ARGS_ARG(1,1));
+  mrb_define_private_method_id(mrb, krn, MRB_SYM(fail), mrb_f_raise, MRB_ARGS_OPT(2));
+  mrb_define_private_method_id(mrb, krn, MRB_SYM(caller), mrb_f_caller, MRB_ARGS_OPT(2));
+  mrb_define_private_method_id(mrb, krn, MRB_SYM(__method__), mrb_f_method, MRB_ARGS_NONE());
+  mrb_define_private_method_id(mrb, krn, MRB_SYM(__callee__), mrb_f_callee, MRB_ARGS_NONE());
+  mrb_define_private_method_id(mrb, krn, MRB_SYM(Integer), mrb_f_integer, MRB_ARGS_ARG(1,1));
 #ifndef MRB_NO_FLOAT
-  mrb_define_module_function_id(mrb, krn, MRB_SYM(Float), mrb_f_float, MRB_ARGS_REQ(1));
+  mrb_define_private_method_id(mrb, krn, MRB_SYM(Float), mrb_f_float, MRB_ARGS_REQ(1));
 #endif
-  mrb_define_module_function_id(mrb, krn, MRB_SYM(String), mrb_f_string, MRB_ARGS_REQ(1));
-  mrb_define_module_function_id(mrb, krn, MRB_SYM(Array), mrb_f_array, MRB_ARGS_REQ(1));
-  mrb_define_module_function_id(mrb, krn, MRB_SYM(Hash), mrb_f_hash, MRB_ARGS_REQ(1));
+  mrb_define_private_method_id(mrb, krn, MRB_SYM(String), mrb_f_string, MRB_ARGS_REQ(1));
+  mrb_define_private_method_id(mrb, krn, MRB_SYM(Array), mrb_f_array, MRB_ARGS_REQ(1));
+  mrb_define_private_method_id(mrb, krn, MRB_SYM(Hash), mrb_f_hash, MRB_ARGS_REQ(1));
 }
 
 void
diff --git a/mrbgems/mruby-kernel-ext/test/kernel.rb b/mrbgems/mruby-kernel-ext/test/kernel.rb
index 0bec08f71..27176f2a0 100644
--- a/mrbgems/mruby-kernel-ext/test/kernel.rb
+++ b/mrbgems/mruby-kernel-ext/test/kernel.rb
@@ -1,6 +1,5 @@
-assert('Kernel.fail, Kernel#fail') do
+assert('Kernel#fail') do
   assert_raise(RuntimeError) { fail }
-  assert_raise(RuntimeError) { Kernel.fail }
 end
 
 assert('Kernel.caller, Kernel#caller') do
@@ -121,10 +120,10 @@ assert('Kernel#String') do
 end
 
 assert('Kernel#Array') do
-  assert_equal([1], Kernel.Array(1))
-  assert_equal([1, 2, 3, 4, 5], Kernel.Array([1, 2, 3, 4, 5]))
-  assert_equal([1, 2, 3, 4, 5], Kernel.Array(1..5))
-  assert_equal([[:a, 1], [:b, 2], [:c, 3]], Kernel.Array({a:1, b:2, c:3}))
+  assert_equal([1], Array(1))
+  assert_equal([1, 2, 3, 4, 5], Array([1, 2, 3, 4, 5]))
+  assert_equal([1, 2, 3, 4, 5], Array(1..5))
+  assert_equal([[:a, 1], [:b, 2], [:c, 3]], Array({a:1, b:2, c:3}))
 end
 
 assert('Kernel#Hash') do