diff --git a/ChangeLog b/ChangeLog
index 6f6b3f9cde..21d8b7ae86 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Sun Jul 17 16:26:40 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* error.c (rb_check_trusted): new function to check an object is
+	  trusted.
+
+	* struct.c (rb_struct_modify), time.c (time_modify): check by the
+	  above function to show proper class names.  [Bug #5036]
+
 Sun Jul 17 15:30:04 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* error.c (rb_warn_m): accept multiple args in like puts.  rdoc
diff --git a/error.c b/error.c
index 53f5472efc..42f83682ea 100644
--- a/error.c
+++ b/error.c
@@ -1714,6 +1714,22 @@ rb_check_frozen(VALUE obj)
     rb_check_frozen_internal(obj);
 }
 
+void
+rb_error_untrusted(VALUE obj)
+{
+    if (rb_safe_level() >= 4) {
+	rb_raise(rb_eSecurityError, "Insecure: can't modify %s",
+		 rb_obj_classname(obj));
+    }
+}
+
+#undef rb_check_trusted
+void
+rb_check_trusted(VALUE obj)
+{
+    rb_check_trusted_internal(obj);
+}
+
 void
 Init_syserr(void)
 {
diff --git a/include/ruby/intern.h b/include/ruby/intern.h
index da1c036740..41a41ea757 100644
--- a/include/ruby/intern.h
+++ b/include/ruby/intern.h
@@ -215,15 +215,24 @@ PRINTF_ARGS(void rb_compile_error_with_enc(const char*, int, void *, const char*
 PRINTF_ARGS(void rb_compile_error_append(const char*, ...), 1, 2);
 NORETURN(void rb_load_fail(const char*));
 NORETURN(void rb_error_frozen(const char*));
+void rb_error_untrusted(VALUE);
 void rb_check_frozen(VALUE);
+void rb_check_trusted(VALUE);
 #define rb_check_frozen_internal(obj) do { \
 	VALUE frozen_obj = (obj); \
 	if (OBJ_FROZEN(frozen_obj)) { \
 	    rb_error_frozen(rb_obj_classname(frozen_obj)); \
 	} \
     } while (0)
+#define rb_check_trusted_internal(obj) do { \
+	VALUE untrusted_obj = (obj); \
+	if (!OBJ_UNTRUSTED(untrusted_obj)) { \
+	    rb_error_untrusted(untrusted_obj); \
+	} \
+    } while (0)
 #ifdef __GNUC__
 #define rb_check_frozen(obj) __extension__({rb_check_frozen_internal(obj);})
+#define rb_check_trusted(obj) __extension__({rb_check_trusted_internal(obj);})
 #else
 static inline void
 rb_check_frozen_inline(VALUE obj)
@@ -231,6 +240,12 @@ rb_check_frozen_inline(VALUE obj)
     rb_check_frozen_internal(obj);
 }
 #define rb_check_frozen(obj) rb_check_frozen_inline(obj)
+static inline void
+rb_check_trusted_inline(VALUE obj)
+{
+    rb_check_trusted_internal(obj);
+}
+#define rb_check_trusted(obj) rb_check_trusted_inline(obj)
 #endif
 
 /* eval.c */
diff --git a/struct.c b/struct.c
index 136ba0acee..ab82fadd1c 100644
--- a/struct.c
+++ b/struct.c
@@ -153,8 +153,7 @@ static void
 rb_struct_modify(VALUE s)
 {
     rb_check_frozen(s);
-    if (!OBJ_UNTRUSTED(s) && rb_safe_level() >= 4)
-       rb_raise(rb_eSecurityError, "Insecure: can't modify Struct");
+    rb_check_trusted(s);
 }
 
 static VALUE
diff --git a/t.rb b/t.rb
new file mode 100755
index 0000000000..757a2b6edf
--- /dev/null
+++ b/t.rb
@@ -0,0 +1,8 @@
+#! /usr/bin/ruby
+tc = Class.new(Time)
+tc.inspect
+t = tc.now
+proc do
+  $SAFE=4
+  t.gmtime
+end.call
diff --git a/test/ruby/test_struct.rb b/test/ruby/test_struct.rb
index 49dcdb45b2..d769e47dc5 100644
--- a/test/ruby/test_struct.rb
+++ b/test/ruby/test_struct.rb
@@ -1,5 +1,6 @@
 require 'test/unit'
 require 'timeout'
+require_relative 'envutil'
 
 class TestStruct < Test::Unit::TestCase
   def test_struct
@@ -249,4 +250,17 @@ class TestStruct < Test::Unit::TestCase
       assert !x.eql?(z)
     }
   end
+
+  def test_struct_subclass
+    bug5036 = '[ruby-dev:44122]'
+    st = Class.new(Struct)
+    s = st.new("S", :m).new
+    error = assert_raise(SecurityError) do
+      proc do
+        $SAFE = 4
+        s.m = 1
+      end.call
+    end
+    assert_equal("Insecure: can't modify #{st}::S", error.message, bug5036)
+  end
 end
diff --git a/test/ruby/test_time.rb b/test/ruby/test_time.rb
index aea4c2edc0..38e567a703 100644
--- a/test/ruby/test_time.rb
+++ b/test/ruby/test_time.rb
@@ -3,6 +3,7 @@ require 'rational'
 require 'delegate'
 require 'timeout'
 require 'delegate'
+require_relative 'envutil'
 
 class TestTime < Test::Unit::TestCase
   def setup
@@ -702,7 +703,7 @@ class TestTime < Test::Unit::TestCase
     bug5012 = "[ruby-dev:44071]"
 
     t0 = Time.now
-    class <<t0; end
+    class << t0; end
     t1 = t0.getlocal
 
     def t0.m
@@ -711,4 +712,18 @@ class TestTime < Test::Unit::TestCase
 
     assert_raise(NoMethodError, bug5012) { t1.m }
   end
+
+  def test_time_subclass
+    bug5036 = '[ruby-dev:44122]'
+    tc = Class.new(Time)
+    tc.inspect
+    t = tc.now
+    error = assert_raise(SecurityError) do
+      proc do
+        $SAFE = 4
+        t.gmtime
+      end.call
+    end
+    assert_equal("Insecure: can't modify #{tc}", error.message, bug5036)
+  end
 end
diff --git a/time.c b/time.c
index b2e3448610..dd846a630c 100644
--- a/time.c
+++ b/time.c
@@ -1876,8 +1876,7 @@ static void
 time_modify(VALUE time)
 {
     rb_check_frozen(time);
-    if (!OBJ_UNTRUSTED(time) && rb_safe_level() >= 4)
-	rb_raise(rb_eSecurityError, "Insecure: can't modify Time");
+    rb_check_trusted(time);
 }
 
 static wideval_t