diff --git a/pkgs/servers/nas/default.nix b/pkgs/servers/nas/default.nix
index 1dba428e0ae9..9b8402ec0e08 100644
--- a/pkgs/servers/nas/default.nix
+++ b/pkgs/servers/nas/default.nix
@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, imake, bison, flex_2_6_1, gccmakedep
+{ stdenv, fetchurl, imake, bison, flex, gccmakedep
 , xproto, libXau, libXt, libXext, libXaw, libXpm, xorgcffiles }:
 
 let
@@ -12,7 +12,7 @@ in stdenv.mkDerivation {
     sha256 = "17dk0ckm6mp1ajc0cd6bwyi638ynw2f6bhbn7gynrs0wfmiyldng";
   };
 
-  nativeBuildInputs = [ imake bison flex_2_6_1 gccmakedep ];
+  nativeBuildInputs = [ imake bison flex gccmakedep ];
 
   buildInputs = [ xproto libXau libXt libXext libXaw libXpm ];
 
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index ef28e8096982..f857cc0183df 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -8510,7 +8510,6 @@ with pkgs;
   jdepend = callPackage ../development/tools/analysis/jdepend { };
 
   flex_2_5_35 = callPackage ../development/tools/parsing/flex/2.5.35.nix { };
-  flex_2_6_1 = callPackage ../development/tools/parsing/flex/2.6.1.nix { };
   flex = callPackage ../development/tools/parsing/flex { };
 
   flexcpp = callPackage ../development/tools/parsing/flexc++ { };