diff --git a/src/xdisp.c b/src/xdisp.c
index 0de5aee86dd..7a164ba2972 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -25067,7 +25067,8 @@ maybe_produce_line_number (struct it *it)
       eassert (it->lnum_width > 0);
     }
   /* Extra +2 for the two blanks we add before and after the number.  */
-  char *lnum_buf = alloca (it->lnum_width + 2 + 1);
+  char *lnum_buf = alloca (max (it->lnum_width, INT_STRLEN_BOUND (ptrdiff_t))
+			   + 2 + 1);
   if (EQ (Vdisplay_line_numbers, Qrelative))
     lnum_offset = it->pt_lnum;
   else if (EQ (Vdisplay_line_numbers, Qvisual))