diff --git a/pkgs/development/tools/parsing/flex/builder-new.sh b/pkgs/development/tools/parsing/flex/builder-new.sh
new file mode 100755
index 00000000000..42ec3fdb375
--- /dev/null
+++ b/pkgs/development/tools/parsing/flex/builder-new.sh
@@ -0,0 +1,10 @@
+#! /bin/sh
+
+export buildinputs="$yacc"
+. $stdenv/setup || exit 1
+
+tar xvfj $src || exit 1
+cd flex-* || exit 1
+./configure --prefix=$out || exit 1
+make || exit 1
+make install || exit 1
diff --git a/pkgs/development/tools/parsing/flex/flex-new.nix b/pkgs/development/tools/parsing/flex/flex-new.nix
new file mode 100644
index 00000000000..fc5d880a027
--- /dev/null
+++ b/pkgs/development/tools/parsing/flex/flex-new.nix
@@ -0,0 +1,18 @@
+# !!! this should be moved to default.nix eventually (but I delay
+# doing that since it would cause a rebuild of lots of stuff).
+
+{stdenv, fetchurl, yacc}:
+
+assert !isNull yacc;
+
+derivation {
+  name = "flex-2.5.31";
+  system = stdenv.system;
+  builder = ./builder-new.sh;
+  src = fetchurl {
+    url = http://heanet.dl.sourceforge.net/sourceforge/lex/flex-2.5.31.tar.bz2;
+    md5 = "363dcc4afc917dc51306eb9d3de0152f";
+  };
+  stdenv = stdenv;
+  yacc = yacc;
+}
diff --git a/pkgs/system/all-packages-generic.nix b/pkgs/system/all-packages-generic.nix
index b7ee646a1c2..f18aba276fb 100644
--- a/pkgs/system/all-packages-generic.nix
+++ b/pkgs/system/all-packages-generic.nix
@@ -209,6 +209,12 @@
     yacc = bison;
   };
 
+  flexnew = (import ../development/tools/parsing/flex/flex-new.nix) {
+    fetchurl = fetchurl;
+    stdenv = stdenv;
+    yacc = bison;
+  };
+
   gcc = (import ../development/compilers/gcc) {
     fetchurl = fetchurl;
     stdenv = stdenv;
diff --git a/pkgs/system/populate-cache.nix b/pkgs/system/populate-cache.nix
index 927a8143839..b4aa946109c 100644
--- a/pkgs/system/populate-cache.nix
+++ b/pkgs/system/populate-cache.nix
@@ -4,6 +4,7 @@ let {
     [ pkgs.zip
       pkgs.unzip
       pkgs.valgrind
+      pkgs.flexnew
       pkgs.par2cmdline
       pkgs.cksfv
       pkgs.graphviz