diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 467d092eab9..8fe3d87190a 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -1679,7 +1679,7 @@ let
            { hurd = gnu.hurdCrossIntermediate; })
     else null;
 
-  ipsecTools = callPackage ../os-specific/linux/ipsec-tools { };
+  ipsecTools = callPackage ../os-specific/linux/ipsec-tools { flex = flex_2_5_35; };
 
   patch = gnupatch;