diff --git a/complex.c b/complex.c
index 2efe6a4..46b9488 100644
--- a/complex.c
+++ b/complex.c
@@ -487,6 +487,8 @@ f_complex_new2(VALUE klass, VALUE x, VALUE y)
 static VALUE
 nucomp_f_complex(int argc, VALUE *argv, VALUE klass)
 {
+    if (argc == 1 && CLASS_OF(argv[0]) == rb_cComplex)
+      return argv[0];
     return rb_funcall2(rb_cComplex, id_convert, argc, argv);
 }
 
diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
index 1435c03..6e06b94 100644
--- a/ext/bigdecimal/bigdecimal.c
+++ b/ext/bigdecimal/bigdecimal.c
@@ -2409,7 +2409,12 @@ BigDecimal_new(int argc, VALUE *argv)
 static VALUE
 BigDecimal_global_new(int argc, VALUE *argv, VALUE self)
 {
-    Real *pv = BigDecimal_new(argc, argv);
+    Real *pv;
+
+    if (argc == 1 && CLASS_OF(argv[0]) == rb_cBigDecimal)
+      return argv[0];
+
+    pv = BigDecimal_new(argc, argv);
     if (ToValue(pv)) pv = VpCopy(NULL, pv);
     pv->obj = TypedData_Wrap_Struct(rb_cBigDecimal, &BigDecimal_data_type, pv);
     return pv->obj;
diff --git a/ext/pathname/pathname.c b/ext/pathname/pathname.c
index 2bb6ce2..59d7e3b 100644
--- a/ext/pathname/pathname.c
+++ b/ext/pathname/pathname.c
@@ -1110,9 +1110,11 @@ path_unlink(VALUE self)
  * Creates a new Pathname object.
  */
 static VALUE
-path_f_pathname(VALUE self, VALUE str)
+path_f_pathname(VALUE self, VALUE arg)
 {
-    return rb_class_new_instance(1, &str, rb_cPathname);
+    if (CLASS_OF(arg) == rb_cPathname)
+      return arg;
+    return rb_class_new_instance(1, &arg, rb_cPathname);
 }
 
 /*
diff --git a/test/bigdecimal/test_bigdecimal.rb b/test/bigdecimal/test_bigdecimal.rb
index a06adb1..0d1965d 100644
--- a/test/bigdecimal/test_bigdecimal.rb
+++ b/test/bigdecimal/test_bigdecimal.rb
@@ -51,6 +51,8 @@ class TestBigDecimal < Test::Unit::TestCase
   def test_global_new
     assert_equal(1, BigDecimal("1"))
     assert_equal(1, BigDecimal("1", 1))
+    bd = BigDecimal.new("1", 1)
+    assert(bd.equal?(BigDecimal(bd)))
     assert_raise(ArgumentError) { BigDecimal("1", -1) }
     assert_raise(ArgumentError) { BigDecimal(4.2) }
     begin
diff --git a/test/pathname/test_pathname.rb b/test/pathname/test_pathname.rb
index ccdc5bd..b218ce0 100644
--- a/test/pathname/test_pathname.rb
+++ b/test/pathname/test_pathname.rb
@@ -437,6 +437,12 @@ class TestPathname < Test::Unit::TestCase
     assert_raise(ArgumentError) { Pathname.new("a\0") }
   end
 
+  def test_global_constructor
+    p = Pathname.new('a')
+    assert_equal(p, Pathname('a'))
+    assert(p.equal?(Pathname(p)))
+  end
+
   class AnotherStringLike # :nodoc:
     def initialize(s) @s = s end
     def to_str() @s end
diff --git a/test/ruby/test_complex.rb b/test/ruby/test_complex.rb
index 0a7828b..5c66476 100644
--- a/test/ruby/test_complex.rb
+++ b/test/ruby/test_complex.rb
@@ -140,6 +140,8 @@ class Complex_Test < Test::Unit::TestCase
     assert_raise(TypeError){Complex(Object.new)}
     assert_raise(ArgumentError){Complex()}
     assert_raise(ArgumentError){Complex(1,2,3)}
+    c = Complex(1,0)
+    assert(c.equal?(Complex(c)))
 
     if (0.0/0).nan?
       assert_nothing_raised{Complex(0.0/0)}