diff --git a/ChangeLog b/ChangeLog
index e2a89940e6..44e7329e30 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,7 @@
-Wed Apr 13 15:50:22 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Wed Apr 13 15:54:36 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* numeric.c (flo_floor): add an optional parameter, digits, as
+	  well as Integer#floor.  [Feature #12245]
 
 	* numeric.c (int_ceil): add an optional parameter, digits, as
 	  well as Integer#round.  [Feature #12245]
diff --git a/numeric.c b/numeric.c
index 53939dce9c..6cf4b181f7 100644
--- a/numeric.c
+++ b/numeric.c
@@ -1727,22 +1727,56 @@ flo_prev_float(VALUE vx)
 
 /*
  *  call-seq:
- *     float.floor  ->  integer
+ *     float.floor([ndigits])  ->  integer or float
  *
- *  Returns the largest integer less than or equal to +float+.
+ *  Returns the largest number less than or equal to +float+ in
+ *  decimal digits (default 0 digits).
+ *
+ *  Precision may be negative.  Returns a floating point number when +ndigits+
+ *  is positive, +self+ for zero, and floor down for negative.
  *
  *     1.2.floor      #=> 1
  *     2.0.floor      #=> 2
  *     (-1.2).floor   #=> -2
  *     (-2.0).floor   #=> -2
+ *
+ *     1.234567.floor(2)  #=> 1.23
+ *     1.234567.floor(3)  #=> 1.234
+ *     1.234567.floor(4)  #=> 1.2345
+ *     1.234567.floor(5)  #=> 1.23456
+ *
+ *     34567.89.floor(-5) #=> 0
+ *     34567.89.floor(-4) #=> 30000
+ *     34567.89.floor(-3) #=> 34000
+ *     34567.89.floor(-2) #=> 34500
+ *     34567.89.floor(-1) #=> 34560
+ *     34567.89.floor(0)  #=> 34567
+ *     34567.89.floor(1)  #=> 34567.8
+ *     34567.89.floor(2)  #=> 34567.89
+ *     34567.89.floor(3)  #=> 34567.89
  */
 
 static VALUE
-flo_floor(VALUE num)
+flo_floor(int argc, VALUE *argv, VALUE num)
 {
-    double f = floor(RFLOAT_VALUE(num));
+    double number, f;
     long val;
+    int ndigits = 0;
 
+    if (rb_check_arity(argc, 0, 1)) {
+	ndigits = NUM2INT(argv[0]);
+    }
+    if (ndigits < 0) {
+	return rb_int_floor(flo_truncate(num), ndigits);
+    }
+    number = RFLOAT_VALUE(num);
+    if (ndigits > 0) {
+	if (float_invariant_round(number, ndigits, &num)) return num;
+	f = pow(10, ndigits);
+	f = floor(number * f) / f;
+	return DBL2NUM(f);
+    }
+    f = floor(number);
     if (!FIXABLE(f)) {
 	return rb_dbl2big(f);
     }
@@ -2028,7 +2062,7 @@ flo_negative_p(VALUE num)
 static VALUE
 num_floor(VALUE num)
 {
-    return flo_floor(rb_Float(num));
+    return flo_floor(0, 0, rb_Float(num));
 }
 
 
@@ -4623,7 +4657,7 @@ Init_Numeric(void)
 
     rb_define_method(rb_cFloat, "to_i", flo_truncate, 0);
     rb_define_method(rb_cFloat, "to_int", flo_truncate, 0);
-    rb_define_method(rb_cFloat, "floor", flo_floor, 0);
+    rb_define_method(rb_cFloat, "floor", flo_floor, -1);
     rb_define_method(rb_cFloat, "ceil", flo_ceil, 0);
     rb_define_method(rb_cFloat, "round", flo_round, -1);
     rb_define_method(rb_cFloat, "truncate", flo_truncate, 0);
diff --git a/test/ruby/test_float.rb b/test/ruby/test_float.rb
index aeac359081..9deed4dea4 100644
--- a/test/ruby/test_float.rb
+++ b/test/ruby/test_float.rb
@@ -444,6 +444,28 @@ class TestFloat < Test::Unit::TestCase
     assert_equal(1.0, 0.998.round(prec))
   end
 
+  def test_floor_with_precision
+    assert_equal(1.100, 1.111.floor(1))
+    assert_equal(1.110, 1.111.floor(2))
+    assert_equal(11110, 11119.9.floor(-1))
+    assert_equal(11100, 11100.0.floor(-2))
+    assert_equal(11100, 11199.9.floor(-2))
+    assert_equal(0, 11111.1.floor(-5))
+
+    assert_equal(10**300, 1.1e300.floor(-300))
+    assert_equal(-2*10**300, -1.1e300.floor(-300))
+    assert_equal(1.0e-300, 1.1e-300.floor(300))
+    assert_equal(-2.0e-300, -1.1e-300.floor(300))
+
+    assert_equal(42.0, 42.0.floor(308))
+    assert_equal(1.0e307, 1.0e307.floor(2))
+
+    assert_raise(TypeError) {1.0.floor("4")}
+    assert_raise(TypeError) {1.0.floor(nil)}
+    def (prec = Object.new).to_int; 2; end
+    assert_equal(0.99, 0.998.floor(prec))
+  end
+
   VS = [
     18446744073709551617.0,
     18446744073709551616.0,