diff --git a/config/install/fillpdf.settings.yml b/config/install/fillpdf.settings.yml
index e45fd62be7822305cc9177a675a7cf87ea0e5964..e42a1291f16b4970b37badf7a1e0aa5dc8cb8cac 100644
--- a/config/install/fillpdf.settings.yml
+++ b/config/install/fillpdf.settings.yml
@@ -2,7 +2,7 @@ allowed_schemes:
   - private
 template_scheme: ''
 
-shell_locale: en_US.utf8
+shell_locale: en_US.UTF-8
 
 remote_protocol: https
 
diff --git a/src/Service/BackendProxy.php b/src/Service/BackendProxy.php
index d548b8bc4b051fb5f3962da7c9d96066dab86f68..193f2b8977316dde42898ce68beb5938ff6cd76d 100644
--- a/src/Service/BackendProxy.php
+++ b/src/Service/BackendProxy.php
@@ -62,6 +62,7 @@ class BackendProxy implements BackendProxyInterface {
     $form_replacements = FillPdfMappingHelper::parseReplacements($fillPdfForm->replacements->value);
 
     $mergeOptions += [
+      'fid' => $fillPdfForm->id(),
       'sample' => FALSE,
       'flatten' => TRUE,
     ];
diff --git a/tests/src/Functional/PdfPopulationTest.php b/tests/src/Functional/PdfPopulationTest.php
index a46c6e8c742f5e8798ee0503008b3780d86b246a..50737d570c914e8a5f9ee9d9aa7cd756753e0c0e 100644
--- a/tests/src/Functional/PdfPopulationTest.php
+++ b/tests/src/Functional/PdfPopulationTest.php
@@ -369,13 +369,16 @@ class PdfPopulationTest extends FillPdfTestBase {
    * Tests PDF population using local service.
    *
    * @throws \PHPUnit_Framework_SkippedTestError
+   * @throws \Behat\Mink\Exception\ResponseTextException
    *   Thrown when test had to be skipped as FillPDF LocalServer is not
    *   available.
+   *
+   * @see \Drupal\Tests\fillpdf\Traits\TestFillPdfTrait::configureLocalServiceBackend()
    */
   public function testMergeLocalService() {
     // For local container testing, we require the Docker container to be
-    // running on port 8085. If http://127.0.0.1:8085/ping does not return a
-    // 200, we assume that we're not in an environment where we can run this
+    // running. If LocalServer's /ping endpoint does not return a 200, we assume
+    // that we're not in an environment where we can run this
     // test.
     $this->configureLocalServiceBackend();
     $config = $this->container->get('config.factory')->get('fillpdf.settings');
@@ -389,6 +392,7 @@ class PdfPopulationTest extends FillPdfTestBase {
    * Tests PDF population using a local install of pdftk.
    *
    * @throws \PHPUnit_Framework_SkippedTestError
+   * @throws \Behat\Mink\Exception\ResponseTextException
    *   Thrown when test had to be skipped as local pdftk install is not
    *   available.
    */
@@ -402,6 +406,8 @@ class PdfPopulationTest extends FillPdfTestBase {
 
   /**
    * Tests a backend.
+   *
+   * @throws \Behat\Mink\Exception\ResponseTextException
    */
   protected function backendTest() {
     // If we can upload a PDF, parsing is working.
@@ -426,11 +432,13 @@ class PdfPopulationTest extends FillPdfTestBase {
       'entity_ids' => ['node' => [$node->id()]],
     ]);
     $this->drupalGet($url);
-    $this->assertSession()->pageTextNotContains('Merging the FillPDF Form failed');
 
     // Check if what we're seeing really is a PDF file.
     $maybe_pdf = $this->getSession()->getPage()->getContent();
     static::assertEquals('application/pdf', $this->getMimeType($maybe_pdf));
+
+    $this->drupalGet('<front>');
+    $this->assertSession()->pageTextNotContains('Merging the FillPDF Form failed');
   }
 
 }
diff --git a/tests/src/Traits/TestFillPdfTrait.php b/tests/src/Traits/TestFillPdfTrait.php
index 52fa369405fac7fd6488fcc3c559baefe909f66b..187fe9d50484231e3fc1e6e973fd6cb38bf2c109 100644
--- a/tests/src/Traits/TestFillPdfTrait.php
+++ b/tests/src/Traits/TestFillPdfTrait.php
@@ -31,11 +31,18 @@ trait TestFillPdfTrait {
     $config_factory = $this->container->get('config.factory');
 
     // Set FillPDF backend and scheme.
-    $config_factory->getEditable('fillpdf.settings')
+    $config = $config_factory->getEditable('fillpdf.settings')
       ->set('allowed_schemes', $configuration['allowed_schemes'])
       ->set('template_scheme', $configuration['template_scheme'])
-      ->set('backend', $configuration['backend'])
-      ->save();
+      ->set('backend', $configuration['backend']);
+
+    // PDFtk needs to have the correct locale set in the environment or the
+    // test will fail.
+    if ($configuration['backend'] === 'pdftk') {
+      $config->set('shell_locale', 'en_US.UTF-8');
+    }
+
+    $config->save();
   }
 
   /**
@@ -44,11 +51,14 @@ trait TestFillPdfTrait {
   protected function configureLocalServiceBackend() {
     // Configure our local filling service. You need to set up your development
     // environment to run the Docker container at http://127.0.0.1:8085 if you
-    // are developing for FillPDF and want to run this test.
+    // are developing for FillPDF and want to run this test. This can be
+    // overridden with the FILLPDF_LOCAL_SERVER environment variable in
+    // phpunit.xml.
+    $localServerEndpoint = getenv('FILLPDF_LOCAL_SERVER');
     $edit = [
       'template_scheme' => 'public',
       'backend' => 'local_service',
-      'local_service_endpoint' => 'http://127.0.0.1:8085',
+      'local_service_endpoint' => $localServerEndpoint ?: 'http://127.0.0.1:8085',
     ];
     $this->drupalPostForm('admin/config/media/fillpdf', $edit, t('Save configuration'));
   }