diff --git a/ChangeLog b/ChangeLog
index 39f066f188..c137bc431d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Wed Nov 16 09:39:27 2011  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* lib/minitest/unit.rb (assert_raises): experimental fix to run
+	  correctly on chkbuild over 64bit linux. call exception_details only
+	  when the detail is really needed to avoid create needless inspect
+	  under ulimit-ed environment.
+
 Wed Nov 16 06:34:30 2011  Tanaka Akira  <akr@fsij.org>
 
 	* test/ruby/test_thread.rb (test_condvar_timed_wait): use
diff --git a/lib/minitest/unit.rb b/lib/minitest/unit.rb
index 38e3f3a83e..677aae767f 100644
--- a/lib/minitest/unit.rb
+++ b/lib/minitest/unit.rb
@@ -357,9 +357,10 @@ module MiniTest
         end
       rescue Exception => e
         details = "#{msg}#{mu_pp(exp)} exception expected, not"
-        assert(exp.any? { |ex|
-                 ex.instance_of?(Module) ? e.kind_of?(ex) : ex == e.class
-               }, exception_details(e, details))
+        bool = exp.any? { |ex|
+          ex.instance_of?(Module) ? e.kind_of?(ex) : ex == e.class
+        }
+        assert(bool, exception_details(e, details)) unless bool
 
         return e
       end