diff --git a/src/Plugin/ContextReaction/JsonldTypeAlterReaction.php b/src/Plugin/ContextReaction/JsonldTypeAlterReaction.php
index b2e757ff..0314e4cd 100644
--- a/src/Plugin/ContextReaction/JsonldTypeAlterReaction.php
+++ b/src/Plugin/ContextReaction/JsonldTypeAlterReaction.php
@@ -89,9 +89,13 @@ class JsonldTypeAlterReaction extends NormalizerAlterReaction {
     $config = $this->getConfiguration();
     $form['source_field'] = [
       '#type' => 'select',
-      '#title' => $this->t('Source Field'),
+      '#title' => $this->t('Field containing RDF type information'),
       '#options' => $options,
-      '#description' => $this->t("Select the field containing the type predicates."),
+      '#description' => $this->t("Use a field to determine the rdf:type. <br/><br/>
+      In JSON-LD representations, the @type attribute (shorthand for rdf:type) will
+      be populated from the value of this field, rather than the default for the bundle
+      as configured in the bundle's RDF mapping. If this field is an entity reference
+      field, the value of the referenced entity's `field_external_uri` will be used."),
       '#default_value' => isset($config['source_field']) ? $config['source_field'] : '',
     ];
     return $form;
diff --git a/tests/src/Functional/JsonldTypeAlterReactionTest.php b/tests/src/Functional/JsonldTypeAlterReactionTest.php
index ce5aa081..d983e36d 100644
--- a/tests/src/Functional/JsonldTypeAlterReactionTest.php
+++ b/tests/src/Functional/JsonldTypeAlterReactionTest.php
@@ -65,7 +65,7 @@ class JsonldTypeAlterReactionTest extends JsonldSelfReferenceReactionTest {
 
     $this->drupalGet("admin/structure/context/$context_name");
     $this->getSession()->getPage()
-      ->fillField("Source Field", "field_type_predicate");
+      ->fillField("Field containing RDF type information", "field_type_predicate");
     $this->getSession()->getPage()->pressButton("Save and continue");
     $this->assertSession()
       ->pageTextContains("The context $context_name has been saved");