diff --git a/src/common/main.c b/src/common/main.c
index b9db34e..0c96e00 100644
--- a/src/common/main.c
+++ b/src/common/main.c
@@ -330,7 +330,7 @@ static void do_attribute(Sheet *cursheet, Key action)
   adj = LEFT;
   do_mark(cursheet, GET_MARK_CUR);
   onecell = SAME_LOC(cursheet->mark1, cursheet->mark2);
-  fcell = CELL_AT(cursheet, cursheet->mark1);
+  fcell = safe_cell_at(cursheet, cursheet->mark1);
   if (action != ADJUST_LOCK && onecell && locked(fcell))
   {
     line_msg(_("Cell attribute:"),_("Cell is locked"));
diff --git a/src/common/sheet.c b/src/common/sheet.c
index cbe3d14..f3f5dd8 100644
--- a/src/common/sheet.c
+++ b/src/common/sheet.c
@@ -446,6 +446,7 @@ void forceupdate(Sheet *sheet)
   Cell *cell;
 
   assert(sheet!=(Sheet*)0);
+  if (sheet->sheet == (Cell **)0) return;
   for (ALL_CELLS_IN_SHEET(sheet,i,cell))
     if (cell != NULLCELL)
       cell->updated = cell->clock_t0 = cell->clock_t1 = cell->clock_t2 = 0;