diff --git a/emacs.nix b/emacs.nix
index ec7da68bb..99c49fa33 100644
--- a/emacs.nix
+++ b/emacs.nix
@@ -1,8 +1,43 @@
 # Derivation for Emacs configured with the packages that I need:
 
-{ pkgs ? import <nixpkgs> {} }:
+{ pkgs ? import <nixos> {} }:
 
 let emacsWithPackages = with pkgs; (emacsPackagesNgGen emacs).emacsWithPackages;
+sly = with pkgs; emacsPackagesNg.melpaBuild {
+  pname   = "sly";
+  version = "20180221.1414";
+
+  src = fetchFromGitHub {
+    owner  = "joaotavora";
+    repo   = "sly";
+    rev    = "486bfbe95612bcdc0960c490207970a188e0fbb9";
+    sha256 = "0ib4q4k3h3qn88pymyjjmlmnpizdn1mfg5gpk5a715nqsgxlg09l";
+  };
+
+  recipeFile = fetchurl {
+    url    = "https://raw.githubusercontent.com/melpa/melpa/23b9e64887a290fca7c7ab2718f627f8d728575f/recipes/sly";
+    sha256 = "1pmyqjk8fdlzwvrlx8h6fq0savksfny78fhmr8r7b07pi20y6n9l";
+    name   = "sly";
+  };
+};
+
+# Building sly-company requires quite some dancing because
+# company-mode is required at build time.
+trivialBuildWithCompany = with pkgs; callPackage <nixos/pkgs/build-support/emacs/trivial.nix> {
+  emacs = with pkgs; emacsWithPackages(epkgs: [ epkgs.elpaPackages.company ]);
+};
+
+sly-company = with pkgs; trivialBuildWithCompany {
+  pname   = "sly-company";
+  version = "master";
+
+  src = fetchFromGitHub {
+    owner  = "joaotavora";
+    repo   = "sly-company";
+    rev    = "dfe18218e4b2ee9874394b50f82f5172f41c462c";
+    sha256 = "1bj8w2wfq944cnhsk5xx41mfrjv89scrg4w98kqgda5drkpdf8a7";
+  };
+};
 
 # Custom code for packages missing from the current Nix packages.
 
@@ -46,8 +81,6 @@ in emacsWithPackages(epkgs:
     rainbow-delimiters
     rust-mode
     s
-    sly
-    sly-company
     smart-mode-line
     string-edit
     terraform-mode
@@ -60,7 +93,9 @@ in emacsWithPackages(epkgs:
     pg
     racket-mode
     restclient
-    sly-quicklisp
     uuidgen
-  ])
+  ]) ++
+
+  # Custom packaged Emacs packages:
+  [ sly sly-company ]
 )