1 files changed, 13 insertions, 0 deletions

diff --git a/src/alloc.c b/src/alloc.c
index 407ac725414..31e8da70161 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -2774,6 +2774,19 @@ DEFUN ("cons", Fcons, Scons, 2, 2, 0,
     {
       if (cons_block_index == CONS_BLOCK_SIZE)
         {
+          /* Maximum number of conses that should be active at any
+             given time, so that list lengths fit into a ptrdiff_t and
+             into a fixnum.  */
+          ptrdiff_t max_conses = min (PTRDIFF_MAX, MOST_POSITIVE_FIXNUM);
+
+          /* This check is typically optimized away, as a runtime
+             check is needed only on weird platforms where a count of
+             distinct conses might not fit.  */
+          if (max_conses < INTPTR_MAX / sizeof (struct Lisp_Cons)
+              && (max_conses - CONS_BLOCK_SIZE
+                  < total_free_conses + total_conses))
+            memory_full (sizeof (struct cons_block));
+
           struct cons_block *new
             = lisp_align_malloc (sizeof *new, MEM_TYPE_CONS);
           memset (new->gcmarkbits, 0, sizeof new->gcmarkbits);