diff --git a/pkgs/development/tools/parsing/flex/default.nix b/pkgs/development/tools/parsing/flex/2.5.39.nix
similarity index 100%
rename from pkgs/development/tools/parsing/flex/default.nix
rename to pkgs/development/tools/parsing/flex/2.5.39.nix
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 64c91fb05bc..16e266b59c1 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -3738,8 +3738,9 @@ let
 
   checkstyle = callPackage ../development/tools/analysis/checkstyle { };
 
-  flex = callPackage ../development/tools/parsing/flex { };
   flex_2_5_35 = callPackage ../development/tools/parsing/flex/2.5.35.nix { };
+  flex_2_5_39 = callPackage ../development/tools/parsing/flex/2.5.39.nix { };
+  flex = flex_2_5_39;
 
   m4 = gnum4;