diff --git a/corepkgs/config.nix.in b/corepkgs/config.nix.in
index 32ce6b399..4ea182d8f 100644
--- a/corepkgs/config.nix.in
+++ b/corepkgs/config.nix.in
@@ -1,3 +1,4 @@
+# FIXME: remove this file?
 let
   fromEnv = var: def:
     let val = builtins.getEnv var; in
@@ -17,13 +18,4 @@ in rec {
   nixLocalstateDir = "@localstatedir@";
   nixSysconfDir = "@sysconfdir@";
   nixStoreDir = fromEnv "NIX_STORE_DIR" "@storedir@";
-
-  # If Nix is installed in the Nix store, then automatically add it as
-  # a dependency to the core packages. This ensures that they work
-  # properly in a chroot.
-  chrootDeps =
-    if dirOf nixPrefix == builtins.storeDir then
-      [ (builtins.storePath nixPrefix) ]
-    else
-      [ ];
 }
diff --git a/corepkgs/unpack-channel.nix b/corepkgs/unpack-channel.nix
index d39a20637..10515bc8b 100644
--- a/corepkgs/unpack-channel.nix
+++ b/corepkgs/unpack-channel.nix
@@ -1,39 +1,12 @@
-with import <nix/config.nix>;
-
-let
-
-  builder = builtins.toFile "unpack-channel.sh"
-    ''
-      mkdir $out
-      cd $out
-      xzpat="\.xz\$"
-      gzpat="\.gz\$"
-      if [[ "$src" =~ $xzpat ]]; then
-        ${xz} -d < $src | ${tar} xf - ${tarFlags}
-      elif [[ "$src" =~ $gzpat ]]; then
-        ${gzip} -d < $src | ${tar} xf - ${tarFlags}
-      else
-        ${bzip2} -d < $src | ${tar} xf - ${tarFlags}
-      fi
-      if [ * != $channelName ]; then
-        mv * $out/$channelName
-      fi
-    '';
-
-in
-
 { name, channelName, src }:
 
 derivation {
-  system = builtins.currentSystem;
-  builder = shell;
-  args = [ "-e" builder ];
-  inherit name channelName src;
+  builder = "builtin:unpack-channel";
 
-  PATH = "${nixBinDir}:${coreutils}";
+  system = "builtin";
+
+  inherit name channelName src;
 
   # No point in doing this remotely.
   preferLocalBuild = true;
-
-  inherit chrootDeps;
 }
diff --git a/nix-rust/src/lib.rs b/nix-rust/src/lib.rs
index 799d52e31..ac6dee543 100644
--- a/nix-rust/src/lib.rs
+++ b/nix-rust/src/lib.rs
@@ -33,7 +33,7 @@ pub extern "C" fn unpack_tarfile(source: Source, dest_dir: &str) -> bool {
     for file in tar.entries().unwrap() {
         let mut file = file.unwrap();
 
-        let dest_file = dest_dir.join(file.header().path().unwrap());
+        let dest_file = dest_dir.join(file.path().unwrap());
 
         fs::create_dir_all(dest_file.parent().unwrap()).unwrap();
 
@@ -55,6 +55,9 @@ pub extern "C" fn unpack_tarfile(source: Source, dest_dir: &str) -> bool {
                     .unwrap();
                 io::copy(&mut file, &mut f).unwrap();
             }
+            tar::EntryType::Symlink => {
+                std::os::unix::fs::symlink(file.header().link_name().unwrap().unwrap(), dest_file).unwrap();
+            }
             t => panic!("Unsupported tar entry type '{:?}'.", t),
         }
     }
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 51a9fa35b..efbb7fc9f 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -3128,6 +3128,8 @@ void DerivationGoal::runChild()
                     builtinFetchurl(drv2, netrcData);
                 else if (drv->builder == "builtin:buildenv")
                     builtinBuildenv(drv2);
+                else if (drv->builder == "builtin:unpack-channel")
+                    builtinUnpackChannel(drv2);
                 else
                     throw Error(format("unsupported builtin function '%1%'") % string(drv->builder, 8));
                 _exit(0);
diff --git a/src/libstore/builtins.hh b/src/libstore/builtins.hh
index 0d2da873e..87d6ce665 100644
--- a/src/libstore/builtins.hh
+++ b/src/libstore/builtins.hh
@@ -7,5 +7,6 @@ namespace nix {
 // TODO: make pluggable.
 void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData);
 void builtinBuildenv(const BasicDerivation & drv);
+void builtinUnpackChannel(const BasicDerivation & drv);
 
 }
diff --git a/src/libstore/builtins/unpack-channel.cc b/src/libstore/builtins/unpack-channel.cc
new file mode 100644
index 000000000..88202ec6b
--- /dev/null
+++ b/src/libstore/builtins/unpack-channel.cc
@@ -0,0 +1,39 @@
+#include "rust.hh"
+#include "builtins.hh"
+#include "compression.hh"
+
+namespace nix {
+
+void builtinUnpackChannel(const BasicDerivation & drv)
+{
+    auto getAttr = [&](const string & name) {
+        auto i = drv.env.find(name);
+        if (i == drv.env.end()) throw Error("attribute '%s' missing", name);
+        return i->second;
+    };
+
+    Path out = getAttr("out");
+    auto channelName = getAttr("channelName");
+    auto src = getAttr("src");
+
+    createDirs(out);
+
+    auto source = sinkToSource([&](Sink & sink) {
+        auto decompressor =
+            hasSuffix(src, ".bz2") ? makeDecompressionSink("bzip2", sink) :
+            hasSuffix(src, ".xz") ? makeDecompressionSink("xz", sink) :
+            makeDecompressionSink("none", sink);
+        readFile(src, *decompressor);
+        decompressor->finish();
+    });
+
+    unpack_tarfile(*source, out);
+
+    auto entries = readDirectory(out);
+    if (entries.size() != 1)
+        throw Error("channel tarball '%s' contains more than one file", src);
+    if (rename((out + "/" + entries[0].name).c_str(), (out + "/" + channelName).c_str()) == -1)
+        throw SysError("renaming channel directory");
+}
+
+}
diff --git a/src/libstore/local.mk b/src/libstore/local.mk
index d690fea28..d3254554d 100644
--- a/src/libstore/local.mk
+++ b/src/libstore/local.mk
@@ -6,7 +6,7 @@ libstore_DIR := $(d)
 
 libstore_SOURCES := $(wildcard $(d)/*.cc $(d)/builtins/*.cc)
 
-libstore_LIBS = libutil
+libstore_LIBS = libutil libnixrust
 
 libstore_LDFLAGS = $(SQLITE3_LIBS) -lbz2 $(LIBCURL_LIBS) $(SODIUM_LIBS) -pthread
 ifneq ($(OS), FreeBSD)
diff --git a/src/nix/test.cc b/src/libstore/rust.hh
similarity index 53%
rename from src/nix/test.cc
rename to src/libstore/rust.hh
index 7f1f0d47a..7e6c2f54d 100644
--- a/src/nix/test.cc
+++ b/src/libstore/rust.hh
@@ -1,9 +1,4 @@
-#include "command.hh"
-#include "store-api.hh"
-#include "common-args.hh"
-#include "compression.hh"
-
-using namespace nix;
+#include "serialise.hh"
 
 namespace rust {
 
@@ -47,37 +42,3 @@ struct Source
 extern "C" {
     bool unpack_tarfile(rust::Source source, rust::StringSlice dest_dir);
 }
-
-struct CmdTest : StoreCommand
-{
-    CmdTest()
-    {
-    }
-
-    std::string name() override
-    {
-        return "test";
-    }
-
-    std::string description() override
-    {
-        return "bla bla";
-    }
-
-    void run(ref<Store> store) override
-    {
-        auto source = sinkToSource([&](Sink & sink) {
-            auto decompressor = makeDecompressionSink("bzip2", sink);
-            readFile("./nix-2.2.tar.bz2", *decompressor);
-            decompressor->finish();
-        });
-
-        std::string destDir = "./dest";
-
-        deletePath(destDir);
-
-        unpack_tarfile(*source, destDir);
-    }
-};
-
-static RegisterCommand r(make_ref<CmdTest>());
diff --git a/src/nix/local.mk b/src/nix/local.mk
index a145cf9b1..c09efd1fc 100644
--- a/src/nix/local.mk
+++ b/src/nix/local.mk
@@ -15,9 +15,9 @@ nix_SOURCES := \
   $(wildcard src/nix-prefetch-url/*.cc) \
   $(wildcard src/nix-store/*.cc) \
 
-nix_LIBS = libexpr libmain libstore libutil libnixrust
+nix_LIBS = libexpr libmain libstore libutil
 
-nix_LDFLAGS = -pthread $(SODIUM_LIBS) $(EDITLINE_LIBS) $(BOOST_LDFLAGS) -lboost_context -lboost_thread -lboost_system -Lnix-rust/target/release
+nix_LDFLAGS = -pthread $(SODIUM_LIBS) $(EDITLINE_LIBS) $(BOOST_LDFLAGS) -lboost_context -lboost_thread -lboost_system
 
 $(foreach name, \
   nix-build nix-channel nix-collect-garbage nix-copy-closure nix-daemon nix-env nix-hash nix-instantiate nix-prefetch-url nix-shell nix-store, \