diff --git a/ChangeLog b/ChangeLog
index 6207b30a5d..9d17e7c279 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+Tue May 31 22:44:00 2011  Kenta Murata  <mrkn@mrkn.jp>
+
+	* ext/bigdecimal/bigdecimal.c (BigDecimal_new): support instantiation a
+	  BigDecimal object from an Integer.
+
+	* test/bigdecimal/test_bigdecimal.rb (test_new_with_integer):
+	  add for testing the above change.
+
+	* ext/bigdecimal/bigdecimal.c (BigDecimal_global_new): replace its body
+	  with a BigDecimal_new call.
+
+	* test/bigdecimal/test_bigdecimal.rb (test_global_new_with_integer):
+	  add for testing the above change.
+
 Tue May 31 22:24:39 2011  Tadayoshi Funaba  <tadf@dotrb.org>
 
 	* ext/date/date_core.c: use simple/complex mode instead of light/right mode.
diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
index 7f64288647..45dac45645 100644
--- a/ext/bigdecimal/bigdecimal.c
+++ b/ext/bigdecimal/bigdecimal.c
@@ -1738,37 +1738,21 @@ BigDecimal_power(VALUE self, VALUE p)
     return ToValue(y);
 }
 
-static VALUE
-BigDecimal_global_new(int argc, VALUE *argv, VALUE self)
-{
-    ENTER(5);
-    Real *pv;
-    size_t mf;
-    VALUE  nFig;
-    VALUE  iniValue;
-
-    if(rb_scan_args(argc,argv,"11",&iniValue,&nFig)==1) {
-	mf = 0;
-    } else {
-	mf = GetPositiveInt(nFig);
-    }
-    SafeStringValue(iniValue);
-    GUARD_OBJ(pv,VpCreateRbObject(mf, RSTRING_PTR(iniValue)));
-    return ToValue(pv);
-}
-
- /* call-seq:
-  * new(initial, digits)
-  *
-  * Create a new BigDecimal object.
-  *
-  * initial:: The initial value, as a String. Spaces are ignored, unrecognized characters terminate the value.
-  *
-  * digits:: The number of significant digits, as a Fixnum. If omitted or 0, the number of significant digits is determined from the initial value.
-  *
-  * The actual number of significant digits used in computation is usually
-  * larger than the specified number.
-  */
+/* call-seq:
+ *   new(initial, digits)
+ *
+ * Create a new BigDecimal object.
+ *
+ * initial:: The initial value, as a String. Spaces are ignored, unrecognized
+ *           characters terminate the value.
+ *
+ * digits:: The number of significant digits, as a Fixnum. If omitted or 0,
+ *          the number of significant digits is determined from the initial
+ *          value.
+ *
+ * The actual number of significant digits used in computation is usually
+ * larger than the specified number.
+ */
 static VALUE
 BigDecimal_new(int argc, VALUE *argv, VALUE self)
 {
@@ -1778,16 +1762,36 @@ BigDecimal_new(int argc, VALUE *argv, VALUE self)
     VALUE  nFig;
     VALUE  iniValue;
 
-    if(rb_scan_args(argc,argv,"11",&iniValue,&nFig)==1) {
+    if (rb_scan_args(argc, argv, "11", &iniValue, &nFig) == 1) {
         mf = 0;
-    } else {
+    }
+    else {
         mf = GetPositiveInt(nFig);
     }
+
+    switch (TYPE(iniValue)) {
+      case T_FIXNUM:
+	/* fall through */
+      case T_BIGNUM:
+	return ToValue(GetVpValue(iniValue, 1));
+
+      case T_STRING:
+	/* fall through */
+      default:
+	break;
+    }
     SafeStringValue(iniValue);
-    GUARD_OBJ(pv,VpNewRbClass(mf, RSTRING_PTR(iniValue),self));
+    GUARD_OBJ(pv, VpNewRbClass(mf, RSTRING_PTR(iniValue),self));
+
     return ToValue(pv);
 }
 
+static VALUE
+BigDecimal_global_new(int argc, VALUE *argv, VALUE self)
+{
+    return BigDecimal_new(argc, argv, rb_cBigDecimal);
+}
+
  /* call-seq:
   * BigDecimal.limit(digits)
   *
diff --git a/test/bigdecimal/test_bigdecimal.rb b/test/bigdecimal/test_bigdecimal.rb
index 810630549b..d50b0e41c3 100644
--- a/test/bigdecimal/test_bigdecimal.rb
+++ b/test/bigdecimal/test_bigdecimal.rb
@@ -29,6 +29,13 @@ class TestBigDecimal < Test::Unit::TestCase
     assert_raise(ArgumentError) { BigDecimal("1", -1) }
   end
 
+  def test_global_new_with_integer
+    assert_equal(BigDecimal("1"), BigDecimal(1))
+    assert_equal(BigDecimal("-1"), BigDecimal(-1))
+    assert_equal(BigDecimal((2**100).to_s), BigDecimal(2**100))
+    assert_equal(BigDecimal((-2**100).to_s), BigDecimal(-2**100))
+  end
+
   def test_new
     assert_equal(1, BigDecimal.new("1"))
     assert_equal(1, BigDecimal.new("1", 1))
@@ -44,6 +51,13 @@ class TestBigDecimal < Test::Unit::TestCase
     assert_equal( 1, BigDecimal.new("1E1111111111111111111").infinite?)
   end
 
+  def test_new_with_integer
+    assert_equal(BigDecimal("1"), BigDecimal.new(1))
+    assert_equal(BigDecimal("-1"), BigDecimal.new(-1))
+    assert_equal(BigDecimal((2**100).to_s), BigDecimal.new(2**100))
+    assert_equal(BigDecimal((-2**100).to_s), BigDecimal.new(-2**100))
+  end
+
   def _test_mode(type)
     BigDecimal.mode(type, true)
     assert_raise(FloatDomainError) { yield }