*** orig/src/window.c
--- mod/src/window.c
***************
*** 607,612 ****
--- 607,616 ----
    int grabbable_width = ux;
    int lmargin_width, rmargin_width, text_left, text_right;
  
+   /* Adjust for the frame's internal border. */
+   *x += FRAME_INTERNAL_BORDER_WIDTH (f);
+   *y += FRAME_INTERNAL_BORDER_WIDTH (f);
+ 
    if (*x < x0 || *x >= x1)
      return ON_NOTHING;