diff --git a/pkgs/servers/x11/xorg/default.nix b/pkgs/servers/x11/xorg/default.nix
index 6f94929ffd67..c9e8dd04c470 100644
--- a/pkgs/servers/x11/xorg/default.nix
+++ b/pkgs/servers/x11/xorg/default.nix
@@ -740,11 +740,11 @@ let
   }) // {inherit windowswmproto libX11 libXext xextproto ;};
 
   libX11 = (mkDerivation "libX11" {
-    name = "libX11-1.6.5";
+    name = "libX11-1.6.6";
     builder = ./builder.sh;
     src = fetchurl {
-      url = mirror://xorg/individual/lib/libX11-1.6.5.tar.bz2;
-      sha256 = "0pa3cfp6h9rl2vxmkph65250gfqyki0ccqyaan6bl9d25gdr0f2d";
+      url = mirror://xorg/individual/lib/libX11-1.6.6.tar.bz2;
+      sha256 = "0ks1mxlda7nxfmffihi15ljsn50q8dknl33i2xag8xzc80fiizk5";
     };
     nativeBuildInputs = [ pkgconfig ];
     buildInputs = [ inputproto kbproto libxcb xextproto xf86bigfontproto xproto xtrans ];
diff --git a/pkgs/servers/x11/xorg/tarballs-7.7.list b/pkgs/servers/x11/xorg/tarballs-7.7.list
index 70f3a35505e0..6e67e8eb6e14 100644
--- a/pkgs/servers/x11/xorg/tarballs-7.7.list
+++ b/pkgs/servers/x11/xorg/tarballs-7.7.list
@@ -60,7 +60,7 @@ mirror://xorg/individual/lib/libICE-1.0.9.tar.bz2
 mirror://xorg/individual/lib/libpciaccess-0.14.tar.bz2
 mirror://xorg/individual/lib/libSM-1.2.2.tar.bz2
 mirror://xorg/X11R7.7/src/everything/libWindowsWM-1.0.1.tar.bz2
-mirror://xorg/individual/lib/libX11-1.6.5.tar.bz2
+mirror://xorg/individual/lib/libX11-1.6.6.tar.bz2
 mirror://xorg/individual/lib/libXau-1.0.8.tar.bz2
 mirror://xorg/individual/lib/libXaw-1.0.13.tar.bz2
 mirror://xorg/individual/lib/libXcomposite-0.4.4.tar.bz2