diff --git a/docs/features/LocalCACertBuilder.md b/docs/features/LocalCACertBuilder.md
index e81f1f3..a9ec263 100644
--- a/docs/features/LocalCACertBuilder.md
+++ b/docs/features/LocalCACertBuilder.md
@@ -62,7 +62,7 @@ use ParagonIE\Certainty\LocalCACertBuilder;
 use ParagonIE\Certainty\RemoteFetch;
 use ParagonIE\ConstantTime\Hex;
 
-$latest = (new RemoteFetch())->getLatestBundle();
+$latest = (new RemoteFetch('/path/to/certainty/data'))->getLatestBundle();
 
 LocalCACertBuilder::fromBundle($latest)
     ->setSigningKey(Hex::decode('your hex-encoded secret key goes here'))
@@ -90,7 +90,7 @@ use ParagonIE\Certainty\LocalCACertBuilder;
 use ParagonIE\Certainty\RemoteFetch;
 use ParagonIE\ConstantTime\Hex;
 
-$latest = (new RemoteFetch())->getLatestBundle();
+$latest = (new RemoteFetch('/path/to/certainty/data'))->getLatestBundle();
 
 /* This snippet is mostly identical from the previous one. */
 LocalCACertBuilder::fromBundle($latest)
diff --git a/docs/features/RemoteFetch.md b/docs/features/RemoteFetch.md
index a4157aa..5258fec 100644
--- a/docs/features/RemoteFetch.md
+++ b/docs/features/RemoteFetch.md
@@ -12,7 +12,7 @@ Using the `RemoteFetch` class is rather straightforward.
 <?php
 use ParagonIE\Certainty\RemoteFetch;
 
-$fetcher = new RemoteFetch();
+$fetcher = new RemoteFetch('/path/to/certainty/data');
 $latestCACertBundle = $fetcher->getLatestBundle();
 
 $ch = curl_init();
@@ -28,7 +28,7 @@ curl_setopt($ch, CURLOPT_CAINFO, $latestCACertBundle->getFilePath());
 use ParagonIE\Certainty\RemoteFetch;
 use GuzzleHttp\Client;
 
-$fetcher = new RemoteFetch();
+$fetcher = new RemoteFetch('/path/to/certainty/data');
 $latestCACertBundle = $fetcher->getLatestBundle();
 $client = new Client();
 
@@ -43,7 +43,7 @@ $response = $client->request('POST', '/url', [
 <?php
 use ParagonIE\Certainty\RemoteFetch;
 
-$fetcher = new RemoteFetch();
+$fetcher = new RemoteFetch('/path/to/certainty/data');
 $latestCACertBundle = $fetcher->getLatestBundle();
 
 $context = stream_context_create([
@@ -93,12 +93,12 @@ object has been created.
 use ParagonIE\Certainty\RemoteFetch;
 
 // Cleaner.
-$fetcher = (new RemoteFetch())
+$fetcher = (new RemoteFetch('/path/to/certainty/data'))
     ->setCacheTimeout(new \DateInterval('PT06H'));
 
 // Alternatively, the constructor approach:
 $fetcher = new RemoteFetch(
-    '',   // use the default save path
+    '/path/to/certainty/data',
     RemoteFetch::DEFAULT_URL,
     null, // automatically selects/configures Guzzle
     new \DateInterval('PT06H') // 6 hours
@@ -117,7 +117,7 @@ Certainty supports this usage.
 <?php
 use ParagonIE\Certainty\RemoteFetch;
 
-$latest = (new RemoteFetch())->getLatestBundle();
+$latest = (new RemoteFetch('/path/to/certainty/data'))->getLatestBundle();
 
 $latest->createSymlink('/path/to/cacert.pem', true);
 ```
diff --git a/src/Certainty.php b/src/Certainty.php
index 95ac35f..a027f76 100644
--- a/src/Certainty.php
+++ b/src/Certainty.php
@@ -25,12 +25,10 @@ class Certainty
      */
     public static function getGuzzleClient(Fetch $fetch = null)
     {
-        if (\is_null($fetch)) {
-            $fetch = new Fetch();
+        $options = [];
+        if (!\is_null($fetch)) {
+            $options['verify'] = $fetch->getLatestBundle()->getFilePath();
         }
-        $options = [
-            'verify' => $fetch->getLatestBundle()->getFilePath()
-        ];
 
         if (\defined('CURLOPT_SSLVERSION') && \defined('CURL_SSLVERSION_TLSv1_2') && \defined('CURL_SSLVERSION_TLSv1')) {
             // https://github.com/curl/curl/blob/6aa86c493bd77b70d1f5018e102bc3094290d588/include/curl/curl.h#L1927
diff --git a/src/Fetch.php b/src/Fetch.php
index 048047a..8dcc4a2 100644
--- a/src/Fetch.php
+++ b/src/Fetch.php
@@ -25,14 +25,15 @@ class Fetch
      * You almost certainly want to use RemoteFetch instead.
      *
      * @param string $dataDir Where the certificates and configuration lives
+     *
+     * @throws FilesystemException
      */
-    public function __construct($dataDir = '')
+    public function __construct($dataDir)
     {
-        if (!empty($dataDir) && \is_readable($dataDir)) {
-            $this->dataDirectory = $dataDir;
-        } else {
-            $this->dataDirectory = \dirname(__DIR__) . '/data';
+        if (!\is_readable($dataDir)) {
+            throw new FilesystemException('Directory is not readable: ' . $dataDir);
         }
+        $this->dataDirectory = $dataDir;
     }
 
     /**
diff --git a/test/BundleTest.php b/test/BundleTest.php
index 852e243..ad6ed94 100644
--- a/test/BundleTest.php
+++ b/test/BundleTest.php
@@ -8,11 +8,17 @@
 
 class BundleTest extends TestCase
 {
+    /**
+     * @var string
+     */
+    protected $defaultDir;
+
     /** @var string $link */
     protected $link;
 
     public function setUp()
     {
+        $this->defaultDir = dirname(__DIR__) . '/data';
         $this->link = __DIR__ . '/static/symlink-test';
     }
 
@@ -37,7 +43,7 @@ public function testCreateSymlink()
             return;
         }
 
-        $latest = (new Fetch())->getLatestBundle();
+        $latest = (new Fetch($this->defaultDir))->getLatestBundle();
 
         $latest->createSymlink($this->link, true);
 
@@ -55,7 +61,7 @@ public function testCreateSymlink()
      */
     public function testGetters()
     {
-        $latest = (new Fetch())->getLatestBundle();
+        $latest = (new Fetch($this->defaultDir))->getLatestBundle();
         $this->assertTrue(\is_string($latest->getFilePath()));
         $this->assertTrue(\is_string($latest->getSha256Sum()));
         $this->assertTrue(\is_string($latest->getSignature()));
diff --git a/test/CustomCASupportTest.php b/test/CustomCASupportTest.php
index 2a10a8e..b082df0 100644
--- a/test/CustomCASupportTest.php
+++ b/test/CustomCASupportTest.php
@@ -13,6 +13,16 @@
  */
 class CustomCASupportTest extends TestCase
 {
+    /**
+     * @var string
+     */
+    protected $defaultDir;
+
+    public function setUp()
+    {
+        $this->defaultDir = dirname(__DIR__) . '/data';
+    }
+
     public function tearDown()
     {
         \unlink(__DIR__ . '/static/combined.pem');
@@ -31,7 +41,7 @@ public function testCustom()
         $validator = new CustomValidator();
         $validator::setPublicKey(Hex::encode($publicKey));
 
-        $latest = (new Fetch())->getLatestBundle();
+        $latest = (new Fetch($this->defaultDir))->getLatestBundle();
         LocalCACertBuilder::fromBundle($latest)
             ->setCustomValidator(CustomValidator::class)
             ->setOutputPemFile(__DIR__ . '/static/combined.pem')
diff --git a/test/FetchTest.php b/test/FetchTest.php
index 9796c95..28e58f7 100644
--- a/test/FetchTest.php
+++ b/test/FetchTest.php
@@ -8,11 +8,17 @@
 
 class FetchTest extends TestCase
 {
+    /**
+     * @var string
+     */
+    protected $defaultDir;
+
     /** @var string */
     protected $root;
 
     public function setUp()
     {
+        $this->defaultDir = dirname(__DIR__) . '/data';
         $this->root = __DIR__ . '/static/';
     }
 
@@ -66,7 +72,7 @@ public function testLiveDataDir()
     {
         $this->assertInstanceOf(
             Bundle::class,
-            (new Fetch())->getLatestBundle(),
+            (new Fetch($this->defaultDir))->getLatestBundle(),
             'The live data directory has no valid signatures.'
         );
     }