diff --git a/pkgs/development/interpreters/acl2/default.nix b/pkgs/development/interpreters/acl2/default.nix
index a0da6e0ee7f8..cc88b32119e7 100644
--- a/pkgs/development/interpreters/acl2/default.nix
+++ b/pkgs/development/interpreters/acl2/default.nix
@@ -4,15 +4,15 @@
 
 let hashes = {
   "8.0" = "1x1giy2c1y6krg3kf8pf9wrmvk981shv0pxcwi483yjqm90xng4r";
-  "8.0.post.2018.09.20" = "1dj1dkkj6drk23h7cckyhcfplyzqlbz288wpxm77zr0gazxz8mw6";
+  "8.1" = "0isi75j94q79x4341rhd94c60228iwvccy71ssnyvh1025m93xcd";
 };
 revs = {
   "8.0" = "8.0";
-  "8.0.post.2018.09.20" = "531089336bb1734ff82c7b3b3fc05917451db770";
+  "8.1" = "8.1";
 };
 in stdenv.mkDerivation rec {
   name = "acl2-${version}";
-  version = "8.0.post.2018.09.20";
+  version = "8.1";
 
   src = fetchFromGitHub {
     owner = "acl2-devel";