diff --git a/HACKING b/HACKING
index e0285b005a3c182143930bf95445a2022c647f71..5c79e9ed8224f703f2504bb1862d05c3d8b5f5fb 100644
--- a/HACKING
+++ b/HACKING
@@ -46,7 +46,7 @@ Bison and flex
 --------------
 
 You may need the Gnu tools bison and flex. The standard lex and yacc
-are not flexible enough. You should have bison version 1.27 or later
+are not flexible enough. You should have bison version 1.35 or later
 and flex version 2.5.4 or later.