diff --git a/io.c b/io.c
index 43f3688..80a10a8 100644
--- a/io.c
+++ b/io.c
@@ -1445,6 +1445,33 @@ rb_io_seek(VALUE io, VALUE offset, int whence)
     return INT2FIX(0);
 }
 
+static VALUE sym_set, sym_cur, sym_current, sym_end;
+
+static int
+sym_to_whence(VALUE ptrname)
+{
+  retry:
+    if (ptrname == sym_set){
+	return SEEK_SET;
+    }
+    else if (ptrname == sym_cur || ptrname == sym_current) {
+	return SEEK_CUR;
+    }
+    else if (ptrname == sym_end) {
+	return SEEK_END;
+    }
+    else {
+	VALUE lower_ptrname;
+
+	lower_ptrname = rb_funcall2(rb_sym_to_s(ptrname), rb_intern("downcase!"), 0, 0);
+	if (!NIL_P(lower_ptrname)) {
+	    ptrname = rb_str_intern(lower_ptrname);
+	    goto retry;
+	}
+    }
+    rb_raise(rb_eArgError, "unknown whence: %s", rb_id2name(SYM2ID(ptrname)));
+}
+
 /*
  *  call-seq:
  *     ios.seek(amount, whence=IO::SEEK_SET)  ->  0
@@ -1473,7 +1500,16 @@ rb_io_seek_m(int argc, VALUE *argv, VALUE io)
     int whence = SEEK_SET;
 
     if (rb_scan_args(argc, argv, "11", &offset, &ptrname) == 2) {
-	whence = NUM2INT(ptrname);
+	switch (TYPE(ptrname)) {
+	  case T_FIXNUM:
+	    whence = NUM2INT(ptrname);
+	    break;
+	  case T_SYMBOL:
+	    whence = sym_to_whence(ptrname);
+	    break;
+	  default:
+	    rb_raise(rb_eTypeError, "type mismatch: %s given", rb_obj_classname(ptrname));
+	}
     }
 
     return rb_io_seek(io, offset, whence);
@@ -11694,4 +11730,8 @@ Init_IO(void)
     sym_willneed = ID2SYM(rb_intern("willneed"));
     sym_dontneed = ID2SYM(rb_intern("dontneed"));
     sym_noreuse = ID2SYM(rb_intern("noreuse"));
+    sym_set = ID2SYM(rb_intern("set"));
+    sym_cur = ID2SYM(rb_intern("cur"));
+    sym_current = ID2SYM(rb_intern("current"));
+    sym_end = ID2SYM(rb_intern("end"));
 }
diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index ddc5f8c..73a16bf 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -1482,6 +1482,72 @@ class TestIO < Test::Unit::TestCase
     }
   end
 
+  def test_seek_sym
+    make_tempfile {|t|
+      open(t.path) { |f|
+        f.seek(9, :set)
+        assert_equal("az\n", f.read)
+      }
+
+      open(t.path) { |f|
+        f.seek(-4, :end)
+        assert_equal("baz\n", f.read)
+      }
+
+      open(t.path) { |f|
+        assert_equal("foo\n", f.gets)
+        f.seek(2, :cur)
+        assert_equal("r\nbaz\n", f.read)
+      }
+
+      open(t.path) { |f|
+        assert_equal("foo\n", f.gets)
+        f.seek(2, :current)
+        assert_equal("r\nbaz\n", f.read)
+      }
+
+      open(t.path) { |f|
+        f.seek(9, :SET)
+        assert_equal("az\n", f.read)
+      }
+
+      open(t.path) { |f|
+        f.seek(-4, :END)
+        assert_equal("baz\n", f.read)
+      }
+
+      open(t.path) { |f|
+        assert_equal("foo\n", f.gets)
+        f.seek(2, :CUR)
+        assert_equal("r\nbaz\n", f.read)
+      }
+
+      open(t.path) { |f|
+        assert_equal("foo\n", f.gets)
+        f.seek(2, :CURRENT)
+        assert_equal("r\nbaz\n", f.read)
+      }
+
+      open(t.path) { |f|
+        assert_raise(ArgumentError) do
+          f.seek(42, :hoge)
+        end
+      }
+
+      open(t.path) { |f|
+        assert_raise(ArgumentError) do
+          f.seek(42, :HOGE)
+        end
+      }
+
+      open(t.path) { |f|
+        assert_raise(TypeError) do
+          f.seek(42, "hoge")
+        end
+      }
+    }
+  end
+
   def test_sysseek
     make_tempfile {|t|
       open(t.path) do |f|