diff --git a/lib/ostruct.rb b/lib/ostruct.rb
index df09cc953f..6b60bdf3fe 100644
--- a/lib/ostruct.rb
+++ b/lib/ostruct.rb
@@ -152,7 +152,7 @@ class OpenStruct
     begin
       @modifiable = true
     rescue
-      raise TypeError, "can't modify frozen #{self.class}", caller(3)
+      raise RuntimeError, "can't modify frozen #{self.class}", caller(3)
     end
     @table
   end
diff --git a/test/ostruct/test_ostruct.rb b/test/ostruct/test_ostruct.rb
index d82bab9784..a472509b88 100644
--- a/test/ostruct/test_ostruct.rb
+++ b/test/ostruct/test_ostruct.rb
@@ -46,14 +46,14 @@ class TC_OpenStruct < Test::Unit::TestCase
     o = OpenStruct.new
     o.a = 'a'
     o.freeze
-    assert_raise(TypeError) {o.b = 'b'}
+    assert_raise(RuntimeError) {o.b = 'b'}
     assert_not_respond_to(o, :b)
-    assert_raise(TypeError) {o.a = 'z'}
+    assert_raise(RuntimeError) {o.a = 'z'}
     assert_equal('a', o.a)
     o = OpenStruct.new :a => 42
     def o.frozen?; nil end
     o.freeze
-    assert_raise(TypeError, '[ruby-core:22559]') {o.a = 1764}
+    assert_raise(RuntimeError, '[ruby-core:22559]') {o.a = 1764}
   end
 
   def test_delete_field