diff --git a/pkgs/tools/package-management/nix/num-cores.patch b/pkgs/tools/package-management/nix/num-cores.patch
new file mode 100644
index 00000000000..1b82631bd30
--- /dev/null
+++ b/pkgs/tools/package-management/nix/num-cores.patch
@@ -0,0 +1,31 @@
+commit b77e3721f19b4e5084125eb8dc7186117004dd4b
+Author: Marc Weber <marco-oweber@gmx.de>
+Date:   Sun Jun 13 23:53:46 2010 +0200
+
+    generic/setup.sh: add -j (+1) -l (*2) options to make depending on $NUM_CORES
+
+diff --git a/pkgs/stdenv/generic/setup.sh b/pkgs/stdenv/generic/setup.sh
+index a9f4d4d..685c0ec 100644
+--- a/pkgs/stdenv/generic/setup.sh
++++ b/pkgs/stdenv/generic/setup.sh
+@@ -79,9 +79,19 @@ cmd(){
+ }
+ 
+ runMake(){
+-  cmd make ${makefile:+-f $makefile} "$@"
++  local optout=NO_PARALLEL_BUILD_${curPhase}
++  [ -n "${!optout}" ] || \
++    local j="$makeFlagsParallelBuild"
++  cmd make ${makefile:+-f $makefile} "$@" $j
+ }
+ 
++######################################################################
++# parallel builds: opt-out
++# - in a phase:     set NO_PARALLEL_BUILD_${PHASE_NAME}
++# - for this build: pass NUM_CORES=1 to the builder
++if [ "$NUM_CORES" -gt 1 ]; then
++  makeFlagsParallelBuild="-j $(( $NUM_CORES + 1 )) -l $(( 2 * $NUM_CORES ))"
++fi
+ 
+ ######################################################################
+ # Initialisation.
diff --git a/pkgs/tools/package-management/nix/unstable.nix b/pkgs/tools/package-management/nix/unstable.nix
index f45172ba426..f1c28d17713 100644
--- a/pkgs/tools/package-management/nix/unstable.nix
+++ b/pkgs/tools/package-management/nix/unstable.nix
@@ -40,4 +40,6 @@ stdenv.mkDerivation rec {
     homepage = http://nixos.org/;
     license = "LGPLv2+";
   };
+
+  patches = [ ./num-cores.patch ];
 }