diff --git a/ChangeLog b/ChangeLog
index 6497a832c5..f6b97785a7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,7 @@
-Fri Dec 10 18:11:08 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Fri Dec 10 18:11:45 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/mkmf.rb (check_signedness): should use the prelude code.
+	  [ruby-dev:42731]
 
 	* lib/mkmf.rb (Logging.log_close): separate from Logging.logfile.
 
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index d289cefca7..c25270dbc6 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -1167,10 +1167,10 @@ end
 # done.
 #
 def check_signedness(type, headers = nil, opts = nil, &b)
-  typedef, member, _ = typedef_expr(type, headers)
+  typedef, member, prelude = typedef_expr(type, headers)
   signed = nil
   checking_for("signedness of #{type}", STRING_OR_FAILED_FORMAT) do
-    signed = try_signedness(typedef, member, headers, opts, &b) or next nil
+    signed = try_signedness(typedef, member, [prelude], opts, &b) or next nil
     $defs.push("-DSIGNEDNESS_OF_%s=%+d" % [type.tr_cpp, signed])
     signed < 0 ? "signed" : "unsigned"
   end
diff --git a/test/mkmf/base.rb b/test/mkmf/base.rb
index 4ceb35087a..f82952d0c5 100644
--- a/test/mkmf/base.rb
+++ b/test/mkmf/base.rb
@@ -13,6 +13,13 @@ class TestMkmf < Test::Unit::TestCase
   class << MKMFLOG
     alias to_s call
   end
+  def mkmflog(msg)
+    log = proc {MKMFLOG[] << msg}
+    class << log
+      alias to_s call
+    end
+    log
+  end
 
   def setup
     @tmpdir = Dir.mktmpdir
diff --git a/test/mkmf/test_signedness.rb b/test/mkmf/test_signedness.rb
new file mode 100644
index 0000000000..97fc1078d6
--- /dev/null
+++ b/test/mkmf/test_signedness.rb
@@ -0,0 +1,27 @@
+require_relative 'base'
+
+class TestMkmf
+  class TestSignedness < TestMkmf
+    def test_typeof_builtin
+      bug4144 = '[ruby-dev:42731]'
+      [["", "-1"], ["signed ", "-1"], ["unsigned ", "+1"]].each do |signed, expect|
+        %w[short int long].each do |type|
+          assert_equal(expect.to_i, mkmf {check_signedness(signed+type)}, mkmflog(bug4144))
+        end
+      end
+    end
+
+    def test_typeof_typedef
+      [["", "-1"], ["signed ", "-1"], ["unsigned ", "+1"]].each do |signed, expect|
+        %w[short int long].each do |type|
+          open("confdefs.h", "w") {|f|
+            f.puts "typedef #{signed}#{type} test1_t;"
+          }
+          $defs.clear
+          assert_equal(expect.to_i, mkmf {check_signedness("test1_t", "confdefs.h")}, MKMFLOG)
+          assert_includes($defs, "-DSIGNEDNESS_OF_TEST1_T=#{expect}")
+        end
+      end
+    end
+  end
+end