diff --git a/src/term.c b/src/term.c
index 0b6d181ff5c..4899efdc121 100644
--- a/src/term.c
+++ b/src/term.c
@@ -3154,9 +3154,13 @@ mouse_get_xy (int *x, int *y)
   struct frame *sf = SELECTED_FRAME ();
   if (f == sf || frame_ancestor_p (sf, f))
     {
-      int mx = XFIXNUM (XCAR (XCDR (mouse)));
-      int my = XFIXNUM (XCDR (XCDR (mouse)));
-      root_xy (f, mx, my, x, y);
+      Lisp_Object lmx = XCAR (XCDR (mouse)), lmy = XCDR (XCDR (mouse));
+      if (FIXNUMP (lmx) && FIXNUMP (lmy))
+	{
+	  int mx = XFIXNUM (lmx);
+	  int my = XFIXNUM (lmy);
+	  root_xy (f, mx, my, x, y);
+	}
     }
 }