diff --git a/src/lib/Hydra/Base/Controller/NixChannel.pm b/src/lib/Hydra/Base/Controller/NixChannel.pm
index 9a815034b..084e755fa 100644
--- a/src/lib/Hydra/Base/Controller/NixChannel.pm
+++ b/src/lib/Hydra/Base/Controller/NixChannel.pm
@@ -29,7 +29,7 @@ sub getChannelData {
         my $outputs = {};
         foreach my $output (@outputs) {
             my $outPath = $output->get_column("outpath");
-            next if $checkValidity && !$BINARY_CACHE_STORE->isValidPath($outPath);
+            next if $checkValidity && !binaryCacheStore()->isValidPath($outPath);
             $outputs->{$output->get_column("outname")} = $outPath;
             push @storePaths, $outPath;
             # Put the system type in the manifest (for top-level
diff --git a/src/lib/Hydra/Controller/Build.pm b/src/lib/Hydra/Controller/Build.pm
index 6d93ef647..ae18d1553 100644
--- a/src/lib/Hydra/Controller/Build.pm
+++ b/src/lib/Hydra/Controller/Build.pm
@@ -79,8 +79,8 @@ sub build_GET {
     # XXX: If the derivation is content-addressed then this will always return
     # false because `$_->path` will be empty
     $c->stash->{available} =
-        all { $_->path && $BINARY_CACHE_STORE->isValidPath($_->path) } $build->buildoutputs->all;
-    $c->stash->{drvAvailable} = $MACHINE_LOCAL_STORE->isValidPath($build->drvpath);
+        all { $_->path && binaryCacheStore()->isValidPath($_->path) } $build->buildoutputs->all;
+    $c->stash->{drvAvailable} = machineLocalStore()->isValidPath($build->drvpath);
 
     if ($build->finished && $build->iscachedbuild) {
         my $path = ($build->buildoutputs)[0]->path or undef;
@@ -304,7 +304,7 @@ sub output : Chained('buildChain') PathPart Args(1) {
     error($c, "This build is not finished yet.") unless $build->finished;
     my $output = $build->buildoutputs->find({name => $outputName});
     notFound($c, "This build has no output named ‘$outputName’") unless defined $output;
-    gone($c, "Output is no longer available.") unless $BINARY_CACHE_STORE->isValidPath($output->path);
+    gone($c, "Output is no longer available.") unless binaryCacheStore()->isValidPath($output->path);
 
     $c->response->header('Content-Disposition', "attachment; filename=\"build-${\$build->id}-${\$outputName}.nar.bz2\"");
     $c->stash->{current_view} = 'NixNAR';
@@ -421,7 +421,7 @@ sub getDependencyGraph {
             };
         $$done{$path} = $node;
         my @refs;
-        foreach my $ref ($BINARY_CACHE_STORE->queryReferences($path)) {
+        foreach my $ref (binaryCacheStore()->queryReferences($path)) {
             next if $ref eq $path;
             next unless $runtime || $ref =~ /\.drv$/;
             getDependencyGraph($self, $c, $runtime, $done, $ref);
@@ -429,7 +429,7 @@ sub getDependencyGraph {
         }
         # Show in reverse topological order to flatten the graph.
         # Should probably do a proper BFS.
-        my @sorted = reverse $BINARY_CACHE_STORE->topoSortPaths(@refs);
+        my @sorted = reverse binaryCacheStore()->topoSortPaths(@refs);
         $node->{refs} = [map { $$done{$_} } @sorted];
     }
 
@@ -442,7 +442,7 @@ sub build_deps : Chained('buildChain') PathPart('build-deps') {
     my $build = $c->stash->{build};
     my $drvPath = $build->drvpath;
 
-    error($c, "Derivation no longer available.") unless $MACHINE_LOCAL_STORE->isValidPath($drvPath);
+    error($c, "Derivation no longer available.") unless machineLocalStore()->isValidPath($drvPath);
 
     $c->stash->{buildTimeGraph} = getDependencyGraph($self, $c, 0, {}, $drvPath);
 
@@ -457,7 +457,7 @@ sub runtime_deps : Chained('buildChain') PathPart('runtime-deps') {
 
     requireLocalStore($c);
 
-    error($c, "Build outputs no longer available.") unless all { $BINARY_CACHE_STORE->isValidPath($_) } @outPaths;
+    error($c, "Build outputs no longer available.") unless all { binaryCacheStore()->isValidPath($_) } @outPaths;
 
     my $done = {};
     $c->stash->{runtimeGraph} = [ map { getDependencyGraph($self, $c, 1, $done, $_) } @outPaths ];
@@ -477,7 +477,7 @@ sub nix : Chained('buildChain') PathPart('nix') CaptureArgs(0) {
     if (isLocalStore) {
         foreach my $out ($build->buildoutputs) {
             notFound($c, "Path " . $out->path . " is no longer available.")
-                unless $BINARY_CACHE_STORE->isValidPath($out->path);
+                unless binaryCacheStore()->isValidPath($out->path);
         }
     }
 
diff --git a/src/lib/Hydra/Controller/Root.pm b/src/lib/Hydra/Controller/Root.pm
index 9d394f2c9..0d8d8dff4 100644
--- a/src/lib/Hydra/Controller/Root.pm
+++ b/src/lib/Hydra/Controller/Root.pm
@@ -395,7 +395,7 @@ sub narinfo :Path :Args(StrMatch[NARINFO_REGEX]) {
         my ($hash) = $narinfo =~ NARINFO_REGEX;
 
         die("Hash length was not 32") if length($hash) != 32;
-        my $path = $BINARY_CACHE_STORE->queryPathFromHashPart($hash);
+        my $path = binaryCacheStore()->queryPathFromHashPart($hash);
 
         if (!$path) {
             $c->response->status(404);
diff --git a/src/lib/Hydra/Helper/Nix.pm b/src/lib/Hydra/Helper/Nix.pm
index 3c3965dfa..84c851a84 100644
--- a/src/lib/Hydra/Helper/Nix.pm
+++ b/src/lib/Hydra/Helper/Nix.pm
@@ -1,5 +1,7 @@
 package Hydra::Helper::Nix;
 
+use feature 'state';
+
 use strict;
 use warnings;
 use Exporter;
@@ -40,12 +42,18 @@ our @EXPORT = qw(
     registerRoot
     restartBuilds
     run
-    $MACHINE_LOCAL_STORE
-    $BINARY_CACHE_STORE
+    machineLocalStore
+    binaryCacheStore
     );
 
-our $MACHINE_LOCAL_STORE = Nix::Store->new();
-our $BINARY_CACHE_STORE = Nix::Store->new(getStoreUri());
+sub machineLocalStore {
+    return Nix::Store->new();
+}
+sub binaryCacheStore {
+    state $binaryCache; # Stores with a custom URL aren't cached by the perl bindings.
+    $binaryCache = Nix::Store->new(getStoreUri()) if not $binaryCache;
+    return $binaryCache;
+}
 
 
 sub getHydraHome {
@@ -499,7 +507,7 @@ sub restartBuilds {
     $builds = $builds->search({ finished => 1 });
 
     foreach my $build ($builds->search({}, { columns => ["drvpath"] })) {
-        next if !$MACHINE_LOCAL_STORE->isValidPath($build->drvpath);
+        next if !machineLocalStore()->isValidPath($build->drvpath);
         registerRoot $build->drvpath;
     }
 
diff --git a/src/lib/Hydra/Plugin/BazaarInput.pm b/src/lib/Hydra/Plugin/BazaarInput.pm
index b35ed7c8c..8c6fada64 100644
--- a/src/lib/Hydra/Plugin/BazaarInput.pm
+++ b/src/lib/Hydra/Plugin/BazaarInput.pm
@@ -37,9 +37,9 @@ sub fetchInput {
     (my $cachedInput) = $self->{db}->resultset('CachedBazaarInputs')->search(
         {uri => $uri, revision => $revision});
 
-    $MACHINE_LOCAL_STORE->addTempRoot($cachedInput->storepath) if defined $cachedInput;
+    machineLocalStore()->addTempRoot($cachedInput->storepath) if defined $cachedInput;
 
-    if (defined $cachedInput && $MACHINE_LOCAL_STORE->isValidPath($cachedInput->storepath)) {
+    if (defined $cachedInput && machineLocalStore()->isValidPath($cachedInput->storepath)) {
         $storePath = $cachedInput->storepath;
         $sha256 = $cachedInput->sha256hash;
     } else {
@@ -57,7 +57,7 @@ sub fetchInput {
         ($sha256, $storePath) = split ' ', $stdout;
 
         # FIXME: time window between nix-prefetch-bzr and addTempRoot.
-        $MACHINE_LOCAL_STORE->addTempRoot($storePath);
+        machineLocalStore()->addTempRoot($storePath);
 
         $self->{db}->txn_do(sub {
             $self->{db}->resultset('CachedBazaarInputs')->create(
diff --git a/src/lib/Hydra/Plugin/DarcsInput.pm b/src/lib/Hydra/Plugin/DarcsInput.pm
index a8df63964..d513f700e 100644
--- a/src/lib/Hydra/Plugin/DarcsInput.pm
+++ b/src/lib/Hydra/Plugin/DarcsInput.pm
@@ -57,7 +57,7 @@ sub fetchInput {
         {uri => $uri, revision => $revision},
         {rows => 1});
 
-    if (defined $cachedInput && $MACHINE_LOCAL_STORE->isValidPath($cachedInput->storepath)) {
+    if (defined $cachedInput && machineLocalStore()->isValidPath($cachedInput->storepath)) {
         $storePath = $cachedInput->storepath;
         $sha256 = $cachedInput->sha256hash;
         $revision = $cachedInput->revision;
@@ -74,8 +74,8 @@ sub fetchInput {
         die "darcs changes --count failed" if $? != 0;
 
         system "rm", "-rf", "$tmpDir/export/_darcs";
-        $storePath = $MACHINE_LOCAL_STORE->addToStore("$tmpDir/export", 1, "sha256");
-        $sha256 = $MACHINE_LOCAL_STORE->queryPathHash($storePath);
+        $storePath = machineLocalStore()->addToStore("$tmpDir/export", 1, "sha256");
+        $sha256 = machineLocalStore()->queryPathHash($storePath);
         $sha256 =~ s/sha256://;
 
         $self->{db}->txn_do(sub {
diff --git a/src/lib/Hydra/Plugin/GitInput.pm b/src/lib/Hydra/Plugin/GitInput.pm
index 0de021282..e1dac085f 100644
--- a/src/lib/Hydra/Plugin/GitInput.pm
+++ b/src/lib/Hydra/Plugin/GitInput.pm
@@ -186,9 +186,9 @@ sub fetchInput {
         {uri => $uri, branch => $branch, revision => $revision, isdeepclone => defined($deepClone) ? 1 : 0},
         {rows => 1});
 
-    $MACHINE_LOCAL_STORE->addTempRoot($cachedInput->storepath) if defined $cachedInput;
+    machineLocalStore()->addTempRoot($cachedInput->storepath) if defined $cachedInput;
 
-    if (defined $cachedInput && $MACHINE_LOCAL_STORE->isValidPath($cachedInput->storepath)) {
+    if (defined $cachedInput && machineLocalStore()->isValidPath($cachedInput->storepath)) {
         $storePath = $cachedInput->storepath;
         $sha256 = $cachedInput->sha256hash;
         $revision = $cachedInput->revision;
@@ -217,7 +217,7 @@ sub fetchInput {
         ($sha256, $storePath) = split ' ', grab(cmd => ["nix-prefetch-git", $clonePath, $revision], chomp => 1);
 
         # FIXME: time window between nix-prefetch-git and addTempRoot.
-        $MACHINE_LOCAL_STORE->addTempRoot($storePath);
+        machineLocalStore()->addTempRoot($storePath);
 
         $self->{db}->txn_do(sub {
             $self->{db}->resultset('CachedGitInputs')->update_or_create(
diff --git a/src/lib/Hydra/Plugin/MercurialInput.pm b/src/lib/Hydra/Plugin/MercurialInput.pm
index 85bd2c708..076489d66 100644
--- a/src/lib/Hydra/Plugin/MercurialInput.pm
+++ b/src/lib/Hydra/Plugin/MercurialInput.pm
@@ -67,9 +67,9 @@ sub fetchInput {
     (my $cachedInput) = $self->{db}->resultset('CachedHgInputs')->search(
         {uri => $uri, branch => $branch, revision => $revision});
 
-    $MACHINE_LOCAL_STORE->addTempRoot($cachedInput->storepath) if defined $cachedInput;
+    machineLocalStore()->addTempRoot($cachedInput->storepath) if defined $cachedInput;
 
-    if (defined $cachedInput && $MACHINE_LOCAL_STORE->isValidPath($cachedInput->storepath)) {
+    if (defined $cachedInput && machineLocalStore()->isValidPath($cachedInput->storepath)) {
         $storePath = $cachedInput->storepath;
         $sha256 = $cachedInput->sha256hash;
     } else {
@@ -84,7 +84,7 @@ sub fetchInput {
         ($sha256, $storePath) = split ' ', $stdout;
 
         # FIXME: time window between nix-prefetch-hg and addTempRoot.
-        $MACHINE_LOCAL_STORE->addTempRoot($storePath);
+        machineLocalStore()->addTempRoot($storePath);
 
         $self->{db}->txn_do(sub {
             $self->{db}->resultset('CachedHgInputs')->update_or_create(
diff --git a/src/lib/Hydra/Plugin/PathInput.pm b/src/lib/Hydra/Plugin/PathInput.pm
index c923a03c3..a69de7fef 100644
--- a/src/lib/Hydra/Plugin/PathInput.pm
+++ b/src/lib/Hydra/Plugin/PathInput.pm
@@ -29,7 +29,7 @@ sub fetchInput {
         {srcpath => $uri, lastseen => {">", $timestamp - $timeout}},
         {rows => 1, order_by => "lastseen DESC"});
 
-    if (defined $cachedInput && $MACHINE_LOCAL_STORE->isValidPath($cachedInput->storepath)) {
+    if (defined $cachedInput && machineLocalStore()->isValidPath($cachedInput->storepath)) {
         $storePath = $cachedInput->storepath;
         $sha256 = $cachedInput->sha256hash;
         $timestamp = $cachedInput->timestamp;
@@ -45,7 +45,7 @@ sub fetchInput {
         }
         chomp $storePath;
 
-        $sha256 = ($MACHINE_LOCAL_STORE->queryPathInfo($storePath, 0))[1] or die;
+        $sha256 = (machineLocalStore()->queryPathInfo($storePath, 0))[1] or die;
 
         ($cachedInput) = $self->{db}->resultset('CachedPathInputs')->search(
             {srcpath => $uri, sha256hash => $sha256});
diff --git a/src/lib/Hydra/Plugin/SubversionInput.pm b/src/lib/Hydra/Plugin/SubversionInput.pm
index 83c1f39d2..484e86051 100644
--- a/src/lib/Hydra/Plugin/SubversionInput.pm
+++ b/src/lib/Hydra/Plugin/SubversionInput.pm
@@ -44,7 +44,7 @@ sub fetchInput {
     (my $cachedInput) = $self->{db}->resultset('CachedSubversionInputs')->search(
         {uri => $uri, revision => $revision});
 
-    $MACHINE_LOCAL_STORE->addTempRoot($cachedInput->storepath) if defined $cachedInput;
+    machineLocalStore()->addTempRoot($cachedInput->storepath) if defined $cachedInput;
 
     if (defined $cachedInput && isValidPath($cachedInput->storepath)) {
         $storePath = $cachedInput->storepath;
@@ -61,16 +61,16 @@ sub fetchInput {
         die "error checking out Subversion repo at `$uri':\n$stderr" if $res;
 
         if ($type eq "svn-checkout") {
-            $storePath = $MACHINE_LOCAL_STORE->addToStore($wcPath, 1, "sha256");
+            $storePath = machineLocalStore()->addToStore($wcPath, 1, "sha256");
         } else {
             # Hm, if the Nix Perl bindings supported filters in
             # addToStore(), then we wouldn't need to make a copy here.
             my $tmpDir = File::Temp->newdir("hydra-svn-export.XXXXXX", CLEANUP => 1, TMPDIR => 1) or die;
             (system "svn", "export", $wcPath, "$tmpDir/source", "--quiet") == 0 or die "svn export failed";
-            $storePath = $MACHINE_LOCAL_STORE->addToStore("$tmpDir/source", 1, "sha256");
+            $storePath = machineLocalStore()->addToStore("$tmpDir/source", 1, "sha256");
         }
 
-        $sha256 = $MACHINE_LOCAL_STORE->queryPathHash($storePath); $sha256 =~ s/sha256://;
+        $sha256 = machineLocalStore()->queryPathHash($storePath); $sha256 =~ s/sha256://;
 
         $self->{db}->txn_do(sub {
             $self->{db}->resultset('CachedSubversionInputs')->update_or_create(
diff --git a/src/lib/Hydra/View/NARInfo.pm b/src/lib/Hydra/View/NARInfo.pm
index bf8711a4a..fa2642acf 100644
--- a/src/lib/Hydra/View/NARInfo.pm
+++ b/src/lib/Hydra/View/NARInfo.pm
@@ -16,7 +16,7 @@ sub process {
 
     $c->response->content_type('text/x-nix-narinfo'); # !!! check MIME type
 
-    my ($deriver, $narHash, $time, $narSize, $refs) = $MACHINE_LOCAL_STORE->queryPathInfo($storePath, 1);
+    my ($deriver, $narHash, $time, $narSize, $refs) = machineLocalStore()->queryPathInfo($storePath, 1);
 
     my $info;
     $info .= "StorePath: $storePath\n";
@@ -27,8 +27,8 @@ sub process {
     $info .= "References: " . join(" ", map { basename $_ } @{$refs}) . "\n";
     if (defined $deriver) {
         $info .= "Deriver: " . basename $deriver . "\n";
-        if ($MACHINE_LOCAL_STORE->isValidPath($deriver)) {
-            my $drv = $MACHINE_LOCAL_STORE->derivationFromPath($deriver);
+        if (machineLocalStore()->isValidPath($deriver)) {
+            my $drv = machineLocalStore()->derivationFromPath($deriver);
             $info .= "System: $drv->{platform}\n";
         }
     }
diff --git a/src/script/hydra-eval-jobset b/src/script/hydra-eval-jobset
index 72a386f57..58e025a22 100755
--- a/src/script/hydra-eval-jobset
+++ b/src/script/hydra-eval-jobset
@@ -85,14 +85,14 @@ sub attrsToSQL {
 # Fetch a store path from 'eval_substituter' if not already present.
 sub getPath {
     my ($path) = @_;
-    return 1 if $MACHINE_LOCAL_STORE->isValidPath($path);
+    return 1 if machineLocalStore()->isValidPath($path);
 
     my $substituter = $config->{eval_substituter};
 
     system("nix", "--experimental-features", "nix-command", "copy", "--from", $substituter, "--", $path)
         if defined $substituter;
 
-    return $MACHINE_LOCAL_STORE->isValidPath($path);
+    return machineLocalStore()->isValidPath($path);
 }
 
 
@@ -143,7 +143,7 @@ sub fetchInputBuild {
         , version => $version
         , outputName => $mainOutput->name
         };
-    if ($MACHINE_LOCAL_STORE->isValidPath($prevBuild->drvpath)) {
+    if (machineLocalStore()->isValidPath($prevBuild->drvpath)) {
         $result->{drvPath} = $prevBuild->drvpath;
     }
 
@@ -233,7 +233,7 @@ sub fetchInputEval {
         my $out = $build->buildoutputs->find({ name => "out" });
         next unless defined $out;
         # FIXME: Should we fail if the path is not valid?
-        next unless $MACHINE_LOCAL_STORE->isValidPath($out->path);
+        next unless machineLocalStore()->isValidPath($out->path);
         $jobs->{$build->get_column('job')} = $out->path;
     }
 
diff --git a/src/script/hydra-update-gc-roots b/src/script/hydra-update-gc-roots
index 130cbb682..5c8050da5 100755
--- a/src/script/hydra-update-gc-roots
+++ b/src/script/hydra-update-gc-roots
@@ -46,7 +46,7 @@ sub keepBuild {
         $build->finished && ($build->buildstatus == 0 || $build->buildstatus == 6))
     {
         foreach my $path (split / /, $build->get_column('outpaths')) {
-            if ($MACHINE_LOCAL_STORE->isValidPath($path)) {
+            if (machineLocalStore()->isValidPath($path)) {
                 addRoot $path;
             } else {
                 print STDERR "    warning: output ", $path, " has disappeared\n" if $build->finished;
@@ -54,7 +54,7 @@ sub keepBuild {
         }
     }
     if (!$build->finished || ($keepFailedDrvs && $build->buildstatus != 0)) {
-        if ($MACHINE_LOCAL_STORE->isValidPath($build->drvpath)) {
+        if (machineLocalStore()->isValidPath($build->drvpath)) {
             addRoot $build->drvpath;
         } else {
             print STDERR "    warning: derivation ", $build->drvpath, " has disappeared\n";