diff --git a/numeric.c b/numeric.c
index e62cb443b9..fbec4d1768 100644
--- a/numeric.c
+++ b/numeric.c
@@ -3380,6 +3380,11 @@ fix_size(VALUE fix)
     return INT2FIX(sizeof(long));
 }
 
+static VALUE
+int_upto_size(VALUE from, VALUE args) {
+    return num_interval_step_size(from, RARRAY_PTR(args)[0], INT2FIX(1), FALSE);
+}
+
 /*
  *  call-seq:
  *     int.upto(limit) {|i| block }  ->  self
@@ -3400,7 +3405,7 @@ fix_size(VALUE fix)
 static VALUE
 int_upto(VALUE from, VALUE to)
 {
-    RETURN_ENUMERATOR(from, 1, &to);
+    RETURN_SIZED_ENUMERATOR(from, 1, &to, int_upto_size);
     if (FIXNUM_P(from) && FIXNUM_P(to)) {
 	long i, end;
 
@@ -3421,6 +3426,11 @@ int_upto(VALUE from, VALUE to)
     return from;
 }
 
+static VALUE
+int_downto_size(VALUE from, VALUE args) {
+    return num_interval_step_size(from, RARRAY_PTR(args)[0], INT2FIX(-1), FALSE);
+}
+
 /*
  *  call-seq:
  *     int.downto(limit) {|i| block }  ->  self
@@ -3442,7 +3452,7 @@ int_upto(VALUE from, VALUE to)
 static VALUE
 int_downto(VALUE from, VALUE to)
 {
-    RETURN_ENUMERATOR(from, 1, &to);
+    RETURN_SIZED_ENUMERATOR(from, 1, &to, int_downto_size);
     if (FIXNUM_P(from) && FIXNUM_P(to)) {
 	long i, end;
 
diff --git a/test/ruby/test_enumerator.rb b/test/ruby/test_enumerator.rb
index 3ce471bb24..fe00aa7e57 100644
--- a/test/ruby/test_enumerator.rb
+++ b/test/ruby/test_enumerator.rb
@@ -543,5 +543,11 @@ class TestEnumerator < Test::Unit::TestCase
     assert_equal Float::INFINITY, (42..Float::INFINITY).step(2).size
     assert_raise(ArgumentError){ (1..10).step(-2).size }
   end
+
+  def test_size_for_downup_to
+    assert_equal 0, 1.upto(-100).size
+    assert_equal 102, 1.downto(-100).size
+    assert_equal Float::INFINITY, 42.upto(Float::INFINITY).size
+  end
 end