diff --git a/core/lib/Drupal/Core/Entity/EntityType.php b/core/lib/Drupal/Core/Entity/EntityType.php
index a4fcf66..ac2fc14 100644
--- a/core/lib/Drupal/Core/Entity/EntityType.php
+++ b/core/lib/Drupal/Core/Entity/EntityType.php
@@ -547,6 +547,10 @@ public function hasLinkTemplate($key) {
    * {@inheritdoc}
    */
   public function setLinkTemplate($key, $path) {
+    if ($path[0] !== '/') {
+      throw new \InvalidArgumentException('Link templates takes path, which have to start with a leading slash.');
+    }
+
     $this->links[$key] = $path;
     return $this;
   }
diff --git a/core/modules/field_ui/field_ui.module b/core/modules/field_ui/field_ui.module
index 6cad751..4cd49f8 100644
--- a/core/modules/field_ui/field_ui.module
+++ b/core/modules/field_ui/field_ui.module
@@ -96,9 +96,9 @@ function field_ui_entity_type_build(array &$entity_types) {
       // This allows us to not require route information inside this hook, which
       // otherwise could result in circular dependencies.
       $entity_type
-        ->setLinkTemplate('field_ui-fields', "admin/{$entity_type->id()}/fields")
-        ->setLinkTemplate('field_ui-form-display', "admin/{$entity_type->id()}/fields-form-display")
-        ->setLinkTemplate('field_ui-display', "admin/{$entity_type->id()}/fields-display");
+        ->setLinkTemplate('field_ui-fields', "/admin/{$entity_type->id()}/fields")
+        ->setLinkTemplate('field_ui-form-display', "/admin/{$entity_type->id()}/fields-form-display")
+        ->setLinkTemplate('field_ui-display', "/admin/{$entity_type->id()}/fields-display");
     }
   }
 }
diff --git a/core/tests/Drupal/Tests/Core/Entity/EntityTypeTest.php b/core/tests/Drupal/Tests/Core/Entity/EntityTypeTest.php
index c6d70ce..c4ae0b6 100644
--- a/core/tests/Drupal/Tests/Core/Entity/EntityTypeTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/EntityTypeTest.php
@@ -241,4 +241,14 @@ protected function getTestHandlerClass() {
     return get_class($this->getMockForAbstractClass('Drupal\Core\Entity\EntityHandlerBase'));
   }
 
+  /**
+   * @covers ::setLinkTemplate
+   *
+   * @expectedException \InvalidArgumentException
+   */
+  public function testSetLinkTemplateWithInvalidPath() {
+    $entity_type = $this->setUpEntityType(['id' => $this->randomMachineName()]);
+    $entity_type->setLinkTemplate('test', 'invalid-path');
+  }
+
 }