diff --git a/NEWS b/NEWS
index 99a239a81..f2b95e7ba 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,9 @@ New in spot 2.10.4.dev  (net yet released)
   - reduce_parity() produced incorrect results when applied to
     automata with deleted edges.
 
+  - work around a portability issue in Flex 2.6.4 preventing
+    compilation on OpenBSD.
+
 New in spot 2.10.4  (2022-02-01)
 
   Bug fixed:
diff --git a/THANKS b/THANKS
index 193dccaf7..9eb566483 100644
--- a/THANKS
+++ b/THANKS
@@ -31,6 +31,7 @@ Joachim Klein
 Juan Tzintzun
 Juraj Major
 Kristin Y. Rozier
+Marc Espie
 Martin Dieguez Lodeiro
 Matthias Heizmann
 Maxime Bouton
diff --git a/spot/parseaut/scanaut.ll b/spot/parseaut/scanaut.ll
index c1c4fb44f..bf35810ed 100644
--- a/spot/parseaut/scanaut.ll
+++ b/spot/parseaut/scanaut.ll
@@ -26,6 +26,14 @@
 /* %option debug */
 %top{
 #include "config.h"
+/* Flex 2.6.4's test for <inttypes.h> relies on __STDC_VERSION__
+   which is undefined in C++.   So without that, it will define
+   its own integer types, including a broken SIZE_MAX definition.
+   So let's define __STDC_VERSION__ to make sure <inttypes.h> gets
+   included. */
+#if HAVE_INTTYPES_H && !(defined __STDC_VERSION__)
+#  define __STDC_VERSION__ 199901L
+#endif
 }
 %{
 #include <string>
diff --git a/spot/parsetl/scantl.ll b/spot/parsetl/scantl.ll
index ff15685f8..554c28298 100644
--- a/spot/parsetl/scantl.ll
+++ b/spot/parsetl/scantl.ll
@@ -1,6 +1,6 @@
 /* -*- coding: utf-8 -*-
-** Copyright (C) 2010-2015, 2017-2019, 2021, Laboratoire de Recherche
-** et Développement de l'Epita (LRDE).
+** Copyright (C) 2010-2015, 2017-2019, 2021-2022, Laboratoire de
+** Recherche et Développement de l'Epita (LRDE).
 ** Copyright (C) 2003, 2004 Laboratoire d'Informatique de Paris 6
 ** (LIP6), département Systèmes Répartis Coopératifs (SRC), Université
 ** Pierre et Marie Curie.
@@ -28,6 +28,14 @@
 
 %top{
 #include "config.h"
+/* Flex 2.6.4's test for <inttypes.h> relies on __STDC_VERSION__
+   which is undefined in C++.   So without that, it will define
+   its own integer types, including a broken SIZE_MAX definition.
+   So let's define __STDC_VERSION__ to make sure <inttypes.h> gets
+   included. */
+#if HAVE_INTTYPES_H && !(defined __STDC_VERSION__)
+#  define __STDC_VERSION__ 199901L
+#endif
 }
 %{
 #include <cstdlib>