diff --git a/src/if_ruby.c b/src/if_ruby.c
index 9474e7c..c1b42e6 100644
--- a/src/if_ruby.c
+++ b/src/if_ruby.c
@@ -1470,7 +1470,7 @@
 
 static VALUE window_width(VALUE self UNUSED)
 {
-    return INT2NUM(get_win(self->w_width));
+    return INT2NUM(get_win(self)->w_width);
 }
 
 static VALUE window_set_width(VALUE self UNUSED, VALUE width)