diff --git a/ChangeLog b/ChangeLog
index 86c51828f9..458129ac2d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Mon Nov  5 22:45:03 2012  Hiroshi Shirosaki  <h.shirosaki@gmail.com>
+
+	* ext/dl/win32/lib/Win32API.rb (Win32API#call): use 64bit pointer for x64
+	  Windows. This would fix
+	  TestSecureRandom#test_s_random_bytes_without_openssl error.
+	  [ruby-core:47451] [Bug #6990]
+
 Mon Nov  5 22:09:26 2012  Hiroshi Shirosaki  <h.shirosaki@gmail.com>
 
 	* cygwin/GNUmakefile.in (uncommon.mk): link *.res.o.
diff --git a/ext/dl/win32/lib/Win32API.rb b/ext/dl/win32/lib/Win32API.rb
index f18cec5749..4d7d4887a5 100644
--- a/ext/dl/win32/lib/Win32API.rb
+++ b/ext/dl/win32/lib/Win32API.rb
@@ -7,6 +7,7 @@ require 'dl'
 class Win32API
   DLL = {}
   TYPEMAP = {"0" => DL::TYPE_VOID, "S" => DL::TYPE_VOIDP, "I" => DL::TYPE_LONG}
+  POINTER_TYPE = DL::SIZEOF_VOIDP == DL::SIZEOF_LONG_LONG ? 'q*' : 'l!*'
 
   def initialize(dllname, func, import, export = "0", calltype = :stdcall)
     @proto = [import].join.tr("VPpNnLlIi", "0SSI").sub(/^(.)0*$/, '\1')
@@ -19,7 +20,7 @@ class Win32API
   def call(*args)
     import = @proto.split("")
     args.each_with_index do |x, i|
-      args[i], = [x == 0 ? nil : x].pack("p").unpack("l!*") if import[i] == "S"
+      args[i], = [x == 0 ? nil : x].pack("p").unpack(POINTER_TYPE) if import[i] == "S"
       args[i], = [x].pack("I").unpack("i") if import[i] == "I"
     end
     ret, = @func.call(args)