diff --git a/easybuild/easyconfigs/f/flex/flex-2.6.4.eb b/easybuild/easyconfigs/f/flex/flex-2.6.4.eb
index 76f531338a8..e15e819b098 100644
--- a/easybuild/easyconfigs/f/flex/flex-2.6.4.eb
+++ b/easybuild/easyconfigs/f/flex/flex-2.6.4.eb
@@ -17,7 +17,7 @@ sources = [SOURCELOWER_TAR_GZ]
 checksums = ['e87aae032bf07c26f85ac0ed3250998c37621d95f8bd748b31f15b33c45ee995']
 
 builddependencies = [
-    ('Bison', '3.3.2'),
+    ('Bison', '3.5.3'),
     ('help2man', '1.47.4'),
 ]