1 files changed, 4 insertions, 2 deletions

diff --git a/src/data.c b/src/data.c
index 7ca1892f64a..3c9152049b7 100644
--- a/src/data.c
+++ b/src/data.c
@@ -3896,12 +3896,14 @@ syms_of_data (void)
   set_symbol_function (Qwholenump, XSYMBOL (Qnatnump)->u.s.function);
 
   DEFVAR_LISP ("most-positive-fixnum", Vmost_positive_fixnum,
-               doc: /* The largest value that is representable in a Lisp integer.  */);
+               doc: /* The largest value that is representable in a Lisp integer.
+This variable cannot be set; trying to do so will signal an error.  */);
   Vmost_positive_fixnum = make_number (MOST_POSITIVE_FIXNUM);
   make_symbol_constant (intern_c_string ("most-positive-fixnum"));
 
   DEFVAR_LISP ("most-negative-fixnum", Vmost_negative_fixnum,
-               doc: /* The smallest value that is representable in a Lisp integer.  */);
+               doc: /* The smallest value that is representable in a Lisp integer.
+This variable cannot be set; trying to do so will signal an error.  */);
   Vmost_negative_fixnum = make_number (MOST_NEGATIVE_FIXNUM);
   make_symbol_constant (intern_c_string ("most-negative-fixnum"));