diff --git a/pkgs/development/libraries/x264/default.nix b/pkgs/development/libraries/x264/default.nix
index 6e4dc00b038..bf32969836c 100644
--- a/pkgs/development/libraries/x264/default.nix
+++ b/pkgs/development/libraries/x264/default.nix
@@ -15,6 +15,11 @@ stdenv.mkDerivation rec {
 
   outputs = [ "out" "lib" ]; # leaving 52 kB of headers
 
+  preConfigure = ''
+    # `AS' is set to the binutils assembler, but we need yasm
+    unset AS
+  '';
+
   configureFlags = [ "--enable-shared" ]
     ++ stdenv.lib.optional (!stdenv.isi686) "--enable-pic"
     ++ stdenv.lib.optional (enable10bit) "--bit-depth=10";