diff --git a/ChangeLog b/ChangeLog
index 2ea6f3b050..6d58663af8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+Mon May  2 01:00:04 2016  Tanaka Akira  <akr@fsij.org>
+
+	* test/lib/test/unit/assertions.rb (assert_fixnum): Defined.
+	  (assert_bignum): Defined.
+
+	* test/ruby/test_bignum.rb: Use assert_bignum.
+
+	* test/ruby/test_integer_comb.rb: Use assert_fixnum and assert_bignum.
+
+	* test/ruby/test_optimization.rb: Ditto.
+
 Mon May  2 00:41:53 2016  Tanaka Akira  <akr@fsij.org>
 
 	* vm_trace.c (recalc_remove_ruby_vm_event_flags): Add a cast to
diff --git a/test/lib/test/unit/assertions.rb b/test/lib/test/unit/assertions.rb
index fd51012fb5..1df3453bc6 100644
--- a/test/lib/test/unit/assertions.rb
+++ b/test/lib/test/unit/assertions.rb
@@ -771,6 +771,14 @@ eom
         values
       end
 
+      def assert_fixnum(v, msg=nil)
+        assert_instance_of(Fixnum, v, msg)
+      end
+
+      def assert_bignum(v, msg=nil)
+        assert_instance_of(Bignum, v, msg)
+      end
+
       class << (AssertFile = Struct.new(:failure_message).new)
         include Assertions
         def assert_file_predicate(predicate, *args)
diff --git a/test/ruby/test_bignum.rb b/test/ruby/test_bignum.rb
index f80828a7a1..762368fda4 100644
--- a/test/ruby/test_bignum.rb
+++ b/test/ruby/test_bignum.rb
@@ -51,18 +51,18 @@ class TestBignum < Test::Unit::TestCase
   end
 
   def test_prepare
-    assert_instance_of(Bignum, @big)
-    assert_instance_of(Bignum, T_ZERO)
-    assert_instance_of(Bignum, T_ONE)
-    assert_instance_of(Bignum, T_MONE)
-    assert_instance_of(Bignum, T31)
-    assert_instance_of(Bignum, T31P)
-    assert_instance_of(Bignum, T32)
-    assert_instance_of(Bignum, T32P)
-    assert_instance_of(Bignum, T64)
-    assert_instance_of(Bignum, T64P)
-    assert_instance_of(Bignum, T1024)
-    assert_instance_of(Bignum, T1024P)
+    assert_bignum(@big)
+    assert_bignum(T_ZERO)
+    assert_bignum(T_ONE)
+    assert_bignum(T_MONE)
+    assert_bignum(T31)
+    assert_bignum(T31P)
+    assert_bignum(T32)
+    assert_bignum(T32P)
+    assert_bignum(T64)
+    assert_bignum(T64P)
+    assert_bignum(T1024)
+    assert_bignum(T1024P)
   end
 
   def test_bignum
@@ -469,7 +469,7 @@ class TestBignum < Test::Unit::TestCase
     assert_raise(TypeError, ArgumentError) { T32**"foo" }
 
     feature3429 = '[ruby-core:30735]'
-    assert_instance_of(Bignum, (2 ** 7830457), feature3429)
+    assert_bignum((2 ** 7830457), feature3429)
   end
 
   def test_and
diff --git a/test/ruby/test_integer_comb.rb b/test/ruby/test_integer_comb.rb
index b18de94feb..8c5cba2b1e 100644
--- a/test/ruby/test_integer_comb.rb
+++ b/test/ruby/test_integer_comb.rb
@@ -114,17 +114,17 @@ class TestIntegerComb < Test::Unit::TestCase
   FIXNUM_MAX = Integer::FIXNUM_MAX
 
   def test_fixnum_range
-    assert_instance_of(Bignum, FIXNUM_MIN-1)
-    assert_instance_of(Fixnum, FIXNUM_MIN)
-    assert_instance_of(Fixnum, FIXNUM_MAX)
-    assert_instance_of(Bignum, FIXNUM_MAX+1)
+    assert_bignum(FIXNUM_MIN-1)
+    assert_fixnum(FIXNUM_MIN)
+    assert_fixnum(FIXNUM_MAX)
+    assert_bignum(FIXNUM_MAX+1)
   end
 
   def check_class(n)
     if FIXNUM_MIN <= n && n <= FIXNUM_MAX
-      assert_instance_of(Fixnum, n)
+      assert_fixnum(n)
     else
-      assert_instance_of(Bignum, n)
+      assert_bignum(n)
     end
   end
 
diff --git a/test/ruby/test_optimization.rb b/test/ruby/test_optimization.rb
index 6412d1f45e..8fd9e208e5 100644
--- a/test/ruby/test_optimization.rb
+++ b/test/ruby/test_optimization.rb
@@ -25,8 +25,8 @@ class TestRubyOptimization < Test::Unit::TestCase
   def test_fixnum_plus
     a, b = 1, 2
     assert_equal 3, a + b
-    assert_instance_of Fixnum, FIXNUM_MAX
-    assert_instance_of Bignum, FIXNUM_MAX + 1
+    assert_fixnum FIXNUM_MAX
+    assert_bignum FIXNUM_MAX + 1
 
     assert_equal 21, 10 + 11
     assert_redefine_method('Fixnum', '+', 'assert_equal 11, 10 + 11')
@@ -34,8 +34,8 @@ class TestRubyOptimization < Test::Unit::TestCase
 
   def test_fixnum_minus
     assert_equal 5, 8 - 3
-    assert_instance_of Fixnum, FIXNUM_MIN
-    assert_instance_of Bignum, FIXNUM_MIN - 1
+    assert_fixnum FIXNUM_MIN
+    assert_bignum FIXNUM_MIN - 1
 
     assert_equal 5, 8 - 3
     assert_redefine_method('Fixnum', '-', 'assert_equal 3, 8 - 3')