diff --git a/src/math-buttons.vala b/src/math-buttons.vala
index 102eedf..3151176 100644
--- a/src/math-buttons.vala
+++ b/src/math-buttons.vala
@@ -429,10 +429,7 @@ public class MathButtons : Gtk.Box
                 button.clicked.connect ((widget) => { equation.insert_digit (widget.get_data<int> ("calc_digit")); });
             }
         }
-        var button = builder.get_object ("calc_subtract_button") as Gtk.Button;
-        if (button != null)
-            button.clicked.connect (() => { equation.insert_subtract (); });
-        button = builder.get_object ("calc_undo_button") as Gtk.Button;
+        var button = builder.get_object ("calc_undo_button") as Gtk.Button;
         if (button != null)
             button.clicked.connect (() => { equation.undo (); });
         button = builder.get_object ("calc_result_button") as Gtk.Button;
