2 files changed, 5 insertions, 2 deletions
diff --git a/test/lib/test/unit.rb b/test/lib/test/unit.rb
index d34e11afa7..df7070e3fc 100644
--- a/test/lib/test/unit.rb
+++ b/test/lib/test/unit.rb
@@ -8,6 +8,7 @@ require 'test/unit/assertions'
 require_relative '../envutil'
 require 'test/unit/testcase'
 require 'optparse'
+require '-test-/testutil'
 
 # See Test::Unit
 module Test
diff --git a/test/lib/test/unit/assertions.rb b/test/lib/test/unit/assertions.rb
index 1df3453bc6..4e30de1be0 100644
--- a/test/lib/test/unit/assertions.rb
+++ b/test/lib/test/unit/assertions.rb
@@ -772,11 +772,13 @@ eom
       end
 
       def assert_fixnum(v, msg=nil)
-        assert_instance_of(Fixnum, v, msg)
+        assert_instance_of(Integer, v, msg)
+        assert_predicate(v, :fixnum?, msg)
       end
 
       def assert_bignum(v, msg=nil)
-        assert_instance_of(Bignum, v, msg)
+        assert_instance_of(Integer, v, msg)
+        assert_predicate(v, :bignum?, msg)
       end
 
       class << (AssertFile = Struct.new(:failure_message).new)