diff --git a/ChangeLog b/ChangeLog
index 0e786ae5d7..b06cdb0608 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+Fri Apr 10 22:29:21 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/mkmf.rb (try_compile): pass the given werror flag to try_do
+	  to check if stderr is empty.
+
+	* lib/mkmf.rb (try_cflags, try_ldflags): default werror to true.
+
+	* win32/Makefile.sub (WERRORFLAG): remove useless option.  VC does
+	  not make warnings of unknown command option an error.
+
 Fri Apr 10 19:34:24 2015  Tanaka Akira  <akr@fsij.org>
 
 	* test/ruby/test_file_exhaustive.rb: Test socket.
diff --git a/ext/date/extconf.rb b/ext/date/extconf.rb
index cb346dfcd9..6f479eaa26 100644
--- a/ext/date/extconf.rb
+++ b/ext/date/extconf.rb
@@ -1,5 +1,5 @@
 require 'mkmf'
-if try_cflags("-std=iso9899:1999", :werror => true)
+if try_cflags("-std=iso9899:1999")
   $CFLAGS += " " << "-std=iso9899:1999"
 end
 create_makefile('date_core')
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index ba3240d0a3..eb95beb2c3 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -568,7 +568,7 @@ MSG
   # [+src+] a String which contains a C source
   # [+opt+] a String which contains compiler options
   def try_compile(src, opt="", *opts, &b)
-    with_werror(opt, *opts) {|_opt, *_opts| try_do(src, cc_command(_opt), *_opts, &b)} and
+    with_werror(opt, *opts) {|_opt, *| try_do(src, cc_command(_opt), *opts, &b)} and
       File.file?("#{CONFTEST}.#{$OBJEXT}")
   ensure
     MakeMakefile.rm_f "#{CONFTEST}*"
@@ -621,8 +621,8 @@ MSG
     $CFLAGS = cflags unless ret
   end
 
-  def try_cflags(flags, *opts)
-    try_compile(MAIN_DOES_NOTHING, flags, *opts)
+  def try_cflags(flags, opts = {})
+    try_compile(MAIN_DOES_NOTHING, flags, {:werror => true}.update(opts))
   end
 
   def with_ldflags(flags)
@@ -633,8 +633,8 @@ MSG
     $LDFLAGS = ldflags unless ret
   end
 
-  def try_ldflags(flags)
-    try_link(MAIN_DOES_NOTHING, flags)
+  def try_ldflags(flags, opts = {})
+    try_link(MAIN_DOES_NOTHING, flags, {:werror => true}.update(opts))
   end
 
   def try_static_assert(expr, headers = nil, opt = "", &b)
diff --git a/win32/Makefile.sub b/win32/Makefile.sub
index 02ec002417..b8bd25bd31 100644
--- a/win32/Makefile.sub
+++ b/win32/Makefile.sub
@@ -208,7 +208,7 @@ WARNFLAGS = -W2 -wd4996 -we4028 -we4142
 WARNFLAGS = -W2
 !endif
 !endif
-WERRORFLAG = -WX -we9002
+WERRORFLAG = -WX
 !if !defined(CFLAGS)
 CFLAGS = $(RUNTIMEFLAG) $(DEBUGFLAGS) $(WARNFLAGS) $(OPTFLAGS) $(PROCESSOR_FLAG) $(COMPILERFLAG)
 !endif