diff --git a/NEWS b/NEWS
index f6cba13cc..1af76aed4 100644
--- a/NEWS
+++ b/NEWS
@@ -1,6 +1,10 @@
 New in spot 2.11.2.dev  (not yet released)
 
-  Nothing yet.
+  Bug fixes:
+
+  - Automata-based implication checks, used to simplify formulas where
+    slower than necessary because the translator was configured to
+    favor determinism unnecessarily.  (Issue #521.)
 
 New in spot 2.11.2  (2022-10-26)
 
diff --git a/THANKS b/THANKS
index db74e14b8..2b054666c 100644
--- a/THANKS
+++ b/THANKS
@@ -23,6 +23,7 @@ Gerard J. Holzmann
 Hashim Ali
 Heikki Tauriainen
 Henrich Lauko
+Jacopo Binchi
 Jan Strejček
 Jean-Michel Couvreur
 Jean-Michel Ilié
diff --git a/spot/tl/simplify.cc b/spot/tl/simplify.cc
index 3a2433197..cbc5857c5 100644
--- a/spot/tl/simplify.cc
+++ b/spot/tl/simplify.cc
@@ -1,5 +1,5 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2011-2021 Laboratoire de Recherche et Developpement
+// Copyright (C) 2011-2022 Laboratoire de Recherche et Developpement
 // de l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
@@ -64,14 +64,14 @@ namespace spot
     }
 
     tl_simplifier_cache(const bdd_dict_ptr& d)
-      : dict(d), lcc(d, true, true, false, false)
+      : dict(d), lcc(d, false, true, false, false)
     {
     }
 
     tl_simplifier_cache(const bdd_dict_ptr& d,
                          const tl_simplifier_options& opt)
       : dict(d), options(opt),
-        lcc(d, true, true, false, false, opt.containment_max_states)
+        lcc(d, false, true, false, false, opt.containment_max_states)
     {
       options.containment_checks |= options.containment_checks_stronger;
       options.event_univ |= options.favor_event_univ;
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 71d6a852f..4c2fe830c 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -222,6 +222,7 @@ TESTS_misc = \
 
 TESTS_twa = \
   core/385.test \
+  core/521.test \
   core/acc.test \
   core/acc2.test \
   core/bdddict.test \
diff --git a/tests/core/521.test b/tests/core/521.test
new file mode 100755
index 000000000..002ab1ca2
--- /dev/null
+++ b/tests/core/521.test
@@ -0,0 +1,64 @@
+#!/bin/sh
+# -*- coding: utf-8 -*-
+# Copyright (C) 2022 Laboratoire de Recherche et Développement de
+# l'Epita (LRDE).
+#
+# This file is part of Spot, a model checking library.
+#
+# Spot is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# Spot is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+# or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+# License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. ./defs
+
+set -e
+
+# For issue #521.
+
+# The following formula used to take hours or days to translate with
+# default settings (nobody was patient enough to wait) because
+# automata-based containment checks were run to exprop=1.
+
+cat >formula.ltl <<'EOF'
+!a & !b & !c & !d & e & f & G(g & h & i & j & ((!c & !d) | (!c & d) |
+(c & !d) | (c & d)) & ((!a & !b) | (!a & b) | (a & !b) | (a & b)) &
+(k -> !l) & (f -> k) & (l -> !k) & (f -> !l) & (l -> !f) & (m -> !n) &
+(m -> o) & (p -> !q) & (m -> !r) & (p -> !m) & (s -> !e) & (r -> !s) &
+(e -> n) & (m -> !t) & (t -> !s) & (q -> u) & (o -> !t) & (m -> !p) &
+(u -> o) & (p -> !v) & (q -> v) & (n -> w) & (x -> !s) & (u -> !t) &
+(p -> w) & (u -> !p) & (t -> n) & (m -> !x) & (q -> !e) & (p -> !u) &
+(s -> !n) & (s -> o) & (s -> m) & (v -> !e) & (x -> n) & (s -> !r) &
+(e -> x) & (e -> !q) & (n -> r) & (w -> !s) & (m -> q) & (s -> !t) &
+(u -> !x) & (e -> p) & (e -> !m) & (s -> !p) & (p -> r) & (e -> !o) &
+(e -> !v) & (t -> x) & (q -> o) & (q -> !n) & (t -> !q) & (r -> !m) &
+(t -> p) & (t -> !m) & (s -> !x) & (v -> o) & (e -> w) & (n -> !s) &
+(q -> !t) & (t -> !o) & (x -> !q) & (e -> !u) & (q -> !p) & (t -> !v) &
+(p -> !s) & (m -> u) & (x -> !m) & (v -> !t) & (s -> q) & (v -> !p) &
+(m -> v) & (r -> w) & (t -> w) & (e -> t) & (e -> r) & (q -> !x) &
+(t -> !u) & (p -> n) & (m -> !e) & (u -> v) & (x -> w) & (o -> !e) &
+(x -> !u) & (s -> !w) & (u -> !e) & (t -> r) & (s -> u) & (e -> !s) &
+(s -> v) & (n -> !q) & (x -> r) & (n -> !m) & (p -> x) & ((!a & !b &
+!c & !d) | (!a & b & !c & d) | (a & !b & c & !d) | (a & b & c & d)) &
+((!c & !d & k & o) -> X(!c & d)) & ((!c & !d & l & v & !(k & o)) ->
+X(!c & d)) & ((!c & !d) -> ((!(k & o) & !(l & v)) -> X(!c & !d))) &
+((!c & d & k & t) -> X(!c & !d)) & ((!c & d & l & p & !(k & t)) -> X(!c
+& !d)) & ((!c & d & k & u & !(l & p & !(k & t))) -> X(c & !d)) & ((!c &
+d & l & q & !(k & u & !(l & p & !(k & t)))) -> X(c & !d)) & ((!c & d) ->
+((!(k & t) & !(l & p) & !(k & u) & !(l & q)) -> X(!c & d))) & ((c & !d
+& k & x) -> X(!c & d)) & ((c & !d & l & n & !(k & x)) -> X(!c & d)) &
+((c & !d & k & m & !(l & n & !(k & x))) -> X(c & d)) & ((c & !d & l &
+s & !(k & m & !(l & n & !(k & x)))) -> X(c & d)) & ((c & !d) -> ((!(k &
+x) & !(l & n) & !(k & m) & !(l & s)) -> X(c & !d))) & ((c & d & k & r)
+-> X(c & !d)) & ((c & d & l & w & !(k & r)) -> X(c & !d)) & ((c & d) ->
+((!(k & r) & !(l & w)) -> X(c & d))))
+EOF
+test 5 = `tr -d "\r\n" < formula.ltl | ltl2tgba --stats=%s`