diff --git a/pkgs/development/libraries/udunits/default.nix b/pkgs/development/libraries/udunits/default.nix
index deed5b64d2c5..b8ea203ef176 100644
--- a/pkgs/development/libraries/udunits/default.nix
+++ b/pkgs/development/libraries/udunits/default.nix
@@ -1,26 +1,49 @@
-{ lib, stdenv, fetchFromGitHub, autoreconfHook,
-  texinfo, bison, flex, expat, file
+{ lib
+, stdenv
+, fetchFromGitHub
+, autoreconfHook
+, bison
+, expat
+, file
+, flex
+, texinfo
 }:
 
 stdenv.mkDerivation rec {
   pname = "udunits";
-  version = "2.2.27.6";
+  version = "unstable-2021-03-17";
 
   src = fetchFromGitHub {
     owner = "Unidata";
     repo = "UDUNITS-2";
-    rev = "v${version}";
-    sha256 = "0621pac24c842dyipzaa59rh6pza9phdqi3snd4cq4pib0wjw6gm";
+    rev = "c83da987387db1174cd2266b73dd5dd556f4476b";
+    hash = "sha256-+HW21+r65OroCxMK2/B5fe7zHs4hD4xyoJK2bhdJGyQ=";
   };
 
-  nativeBuildInputs = [ autoreconfHook texinfo bison flex file ];
-  buildInputs = [ expat ];
+  nativeBuildInputs = [
+    autoreconfHook
+    texinfo
+    bison
+    flex
+    file
+  ];
+  buildInputs = [
+    expat
+  ];
 
   meta = with lib; {
     homepage = "https://www.unidata.ucar.edu/software/udunits/";
     description = "A C-based package for the programatic handling of units of physical quantities";
-    license = licenses.bsdOriginal;
+    longDescription = ''
+      The UDUNITS package supports units of physical quantities. Its C library
+      provides for arithmetic manipulation of units and for conversion of
+      numeric values between compatible units. The package contains an extensive
+      unit database, which is in XML format and user-extendable. The package
+      also contains a command-line utility for investigating units and
+      converting values.
+    '';
+    license = licenses.asl20;
+    maintainers = with maintainers; [ AndersonTorres pSub ];
     platforms = platforms.linux;
-    maintainers = with maintainers; [ pSub ];
   };
 }