diff --git a/pkgs/applications/editors/emacs/default.nix b/pkgs/applications/editors/emacs/default.nix
index 4a729ba3da3..08223ef82ef 100644
--- a/pkgs/applications/editors/emacs/default.nix
+++ b/pkgs/applications/editors/emacs/default.nix
@@ -6,6 +6,7 @@
 , withGTK2 ? true, gtk2 ? null
 , withGTK3 ? false, gtk3 ? null
 , withXwidgets ? false, webkitgtk24x ? null, wrapGAppsHook ? null, glib_networking ? null
+, withCsrc ? true
 , srcRepo ? false, autoconf ? null, automake ? null, texinfo ? null
 }:
 
@@ -24,7 +25,9 @@ let
     else "lucid";
 in
 stdenv.mkDerivation rec {
-  name = "emacs-25.1";
+  name = "emacs-${version}${versionModifier}";
+  version = "25.1";
+  versionModifier = "";
 
   src = fetchurl {
     url = "mirror://gnu//emacs/${name}.tar.xz";
@@ -71,9 +74,23 @@ stdenv.mkDerivation rec {
     done
   '';
 
+  installTargets = "tags install";
+
   postInstall = ''
-    mkdir -p $out/share/emacs/site-lisp/
+    mkdir -p $out/share/emacs/site-lisp
     cp ${./site-start.el} $out/share/emacs/site-lisp/site-start.el
+    $out/bin/emacs --batch -f batch-byte-compile $out/share/emacs/site-lisp/site-start.el
+
+    rm -rf $out/var
+    rm -rf $out/share/emacs/${version}/site-lisp
+  '' + lib.optionalString withCsrc ''
+    for srcdir in src lisp lwlib ; do
+      dstdir=$out/share/emacs/${version}/$srcdir
+      mkdir -p $dstdir
+      find $srcdir -name "*.[chm]" -exec cp {} $dstdir \;
+      cp $srcdir/TAGS $dstdir
+      echo '((nil . ((tags-file-name . "TAGS"))))' > $dstdir/.dir-locals.el
+    done
   '' + lib.optionalString stdenv.isDarwin ''
     mkdir -p $out/Applications
     mv nextstep/Emacs.app $out/Applications
diff --git a/pkgs/applications/editors/emacs/site-start.el b/pkgs/applications/editors/emacs/site-start.el
index 023d6412ed8..b41ca92db08 100644
--- a/pkgs/applications/editors/emacs/site-start.el
+++ b/pkgs/applications/editors/emacs/site-start.el
@@ -1,4 +1,4 @@
-;; NixOS specific load-path
+;;; NixOS specific load-path
 (setq load-path
       (append (reverse (mapcar (lambda (x) (concat x "/share/emacs/site-lisp/"))
                                (split-string (or (getenv "NIX_PROFILES") ""))))
@@ -11,7 +11,25 @@
                                   (split-string (or (getenv "NIX_PROFILES") ""))))
                  woman-manpath)))
 
-;; Make tramp work for remote NixOS machines
-;;; NOTE: You might want to add 
+;;; Make tramp work for remote NixOS machines
 (eval-after-load 'tramp
   '(add-to-list 'tramp-remote-path "/run/current-system/sw/bin"))
+
+;;; C source directory
+;;;
+;;; Computes the location of the C source directory from the path of
+;;; the current file:
+;;; from: /nix/store/<hash>-emacs-<version>/share/emacs/site-lisp/site-start.el
+;;; to:   /nix/store/<hash>-emacs-<version>/share/emacs/<version>/src/
+(let ((emacs
+       (file-name-directory                      ;; .../emacs/
+        (directory-file-name                     ;; .../emacs/site-lisp
+         (file-name-directory load-file-name)))) ;; .../emacs/site-lisp/
+      (version
+       (file-name-as-directory
+        (concat
+         (number-to-string emacs-major-version)
+         "."
+         (number-to-string emacs-minor-version))))
+      (src (file-name-as-directory "src")))
+  (setq find-function-C-source-directory (concat emacs version src)))
diff --git a/pkgs/build-support/emacs/wrapper.nix b/pkgs/build-support/emacs/wrapper.nix
index 45931e6914a..b13def07bb8 100644
--- a/pkgs/build-support/emacs/wrapper.nix
+++ b/pkgs/build-support/emacs/wrapper.nix
@@ -85,13 +85,14 @@ stdenv.mkDerivation {
      done
 
      siteStart="$out/share/emacs/site-lisp/site-start.el"
+     siteStartByteCompiled="$siteStart"c
 
      # A dependency may have brought the original siteStart, delete it and
      # create our own
      # Begin the new site-start.el by loading the original, which sets some
      # NixOS-specific paths. Paths are searched in the reverse of the order
      # they are specified in, so user and system profile paths are searched last.
-     rm -f $siteStart
+     rm -f $siteStart $siteStartByteCompiled
      cat >"$siteStart" <<EOF
 (load-file "$emacs/share/emacs/site-lisp/site-start.el")
 (add-to-list 'load-path "$out/share/emacs/site-lisp")
diff --git a/pkgs/top-level/emacs-packages.nix b/pkgs/top-level/emacs-packages.nix
index 1e878e8b18c..430da89fc22 100644
--- a/pkgs/top-level/emacs-packages.nix
+++ b/pkgs/top-level/emacs-packages.nix
@@ -189,30 +189,6 @@ let
     };
   };
 
-  emacs-source-directory = stdenv.mkDerivation {
-    name = "emacs-source-directory-1.0.0";
-    src = emacs.src;
-
-    # We don't want accidentally start bulding emacs one more time
-    phases = "unpackPhase buildPhase";
-
-    buildPhase = ''
-     mkdir -p $out/share/emacs/site-lisp/elpa/emacs-source-directory
-     cp -a src $out/src
-     (cd $out/src && ${emacs}/bin/etags *.c *.h)
-     cat <<EOF > $out/share/emacs/site-lisp/elpa/emacs-source-directory/emacs-source-directory-autoloads.el
-     (setq source-directory "$out")
-     (setq find-function-C-source-directory (expand-file-name "src" source-directory))
-     EOF
-     cat <<EOF > $out/share/emacs/site-lisp/elpa/emacs-source-directory/emacs-source-directory-pkg.el
-     (define-package "emacs-source-directory" "1.0.0" "Make emacs C source code available inside emacs. To use with emacsWithPackages in NixOS" '())
-     EOF
-    '';
-    meta = {
-      description = "Make emacs C source code available inside emacs. To use with emacsWithPackages in NixOS";
-    };
-  };
-
   evil-jumper = melpaBuild rec {
     pname   = "evil-jumper";
     version = "20151017";