diff --git a/enum.c b/enum.c
index 609438bfdb..56cef1726d 100644
--- a/enum.c
+++ b/enum.c
@@ -2527,10 +2527,15 @@ enum_each_slice_size(VALUE obj, VALUE args, VALUE eobj)
 {
     VALUE n, size;
     long slice_size = NUM2LONG(RARRAY_AREF(args, 0));
+    ID infinite_p;
+    CONST_ID(infinite_p, "infinite?");
     if (slice_size <= 0) rb_raise(rb_eArgError, "invalid slice size");
 
     size = enum_size(obj, 0, 0);
     if (size == Qnil) return Qnil;
+    if (RB_FLOAT_TYPE_P(size) && RTEST(rb_funcall(size, infinite_p, 0))) {
+        return size;
+    }
 
     n = add_int(size, slice_size-1);
     return div_int(n, slice_size);
diff --git a/test/ruby/test_enumerator.rb b/test/ruby/test_enumerator.rb
index 6bc776dee5..54dfebb814 100644
--- a/test/ruby/test_enumerator.rb
+++ b/test/ruby/test_enumerator.rb
@@ -113,6 +113,11 @@ class TestEnumerator < Test::Unit::TestCase
     assert_equal([[1,2,3],[4,5,6],[7,8,9],[10]], (1..10).each_slice(3).to_a)
   end
 
+  def test_each_slice_size
+    assert_equal(4, (1..10).each_slice(3).size)
+    assert_equal(Float::INFINITY, 1.step.each_slice(3).size)
+  end
+
   def test_cons
     a = [[1,2,3], [2,3,4], [3,4,5], [4,5,6], [5,6,7], [6,7,8], [7,8,9], [8,9,10]]
     assert_equal(a, (1..10).each_cons(3).to_a)