diff --git a/struct.c b/struct.c
index 136ba0a..d478013 100644
--- a/struct.c
+++ b/struct.c
@@ -154,7 +154,7 @@ 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_raise(rb_eSecurityError, "Insecure: can't modify %s", rb_obj_classname(s));
 }
 
 static VALUE
diff --git a/time.c b/time.c
index b2e3448..91e912b 100644
--- a/time.c
+++ b/time.c
@@ -1877,7 +1877,7 @@ 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_raise(rb_eSecurityError, "Insecure: can't modify %s", rb_obj_classname(time));
 }
 
 static wideval_t
diff --git a/test/ruby/test_struct.rb b/test/ruby/test_struct.rb
index 49dcdb4..ff9ec32 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
+    bugNNNN = '[ruby-dev:NNNN]'
+    assert_in_out_err([], <<-INPUT, [], /Insecure: can't modify Struct2::S \(SecurityError\)$/, bugNNNN)
+      Thread.new do
+        class Struct2 < Struct
+        end
+        s = Struct2.new("S", :m).new
+        $SAFE=4
+        s.m=1
+      end.join
+    INPUT
+  end
 end
diff --git a/test/ruby/test_time.rb b/test/ruby/test_time.rb
index aea4c2e..d30ceda 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
@@ -711,4 +712,17 @@ class TestTime < Test::Unit::TestCase
 
     assert_raise(NoMethodError, bug5012) { t1.m }
   end
+
+  def test_time_subclass
+    bugNNNN = '[ruby-dev:NNNN]'
+    assert_in_out_err([], <<-INPUT, [], /Insecure: can't modify Time2 \(SecurityError\)$/, bugNNNN)
+      Thread.new do
+        class Time2 < Time
+        end
+        t = Time2.now
+        $SAFE=4
+        t.gmtime
+      end.join
+    INPUT
+  end
 end