diff --git a/pkgs/development/libraries/liblastfm/default.nix b/pkgs/development/libraries/liblastfm/default.nix
index 57a325a7234..24b93221d11 100644
--- a/pkgs/development/libraries/liblastfm/default.nix
+++ b/pkgs/development/libraries/liblastfm/default.nix
@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, ruby, qt4, pkgconfig, libsamplerate, fftwSinglePrec }:
+{ stdenv, fetchurl, ruby, qt4, pkgconfig, libsamplerate, fftwSinglePrec, which }:
 
 let version = "0.3.3"; in
 
@@ -14,7 +14,7 @@ stdenv.mkDerivation rec {
 
   prefixKey = "--prefix ";
   propagatedBuildInputs = [ qt4 libsamplerate fftwSinglePrec ];
-  buildNativeInputs = [ ruby pkgconfig ];
+  buildNativeInputs = [ ruby pkgconfig which ];
 
   configureFlags = "--release";
 
diff --git a/pkgs/development/libraries/libpng/default.nix b/pkgs/development/libraries/libpng/default.nix
index 7ba9bfb54b3..04872d3b431 100644
--- a/pkgs/development/libraries/libpng/default.nix
+++ b/pkgs/development/libraries/libpng/default.nix
@@ -4,11 +4,11 @@ assert zlib != null;
 
 # If you want to upgrade libpng, look at libpng15 branch
 stdenv.mkDerivation rec {
-  name = "libpng-1.2.46";
+  name = "libpng-1.2.47";
   
   src = fetchurl {
     url = "mirror://sourceforge/libpng/${name}.tar.xz";
-    sha256 = "0rcx4v4khdkrvz7b02fmx7lab2pk1lal4dhx9widv36b7g2xvwzn";
+    sha256 = "1lai3dnzw81y40jr17bdj1qh08hwv9mc1v74yybl7jdx2hiilsvx";
   };
   
   propagatedBuildInputs = [ zlib ];