diff --git a/modules/taxonomy/taxonomy.pages.inc b/modules/taxonomy/taxonomy.pages.inc
index 2630413..3714ca3 100644
--- a/modules/taxonomy/taxonomy.pages.inc
+++ b/modules/taxonomy/taxonomy.pages.inc
@@ -108,7 +108,13 @@ function taxonomy_term_feed($term) {
  * @see taxonomy_field_widget_info()
  */
 function taxonomy_autocomplete($field_name, $tags_typed = '') {
-  $field = field_info_field($field_name);
+  // Make sure the field exists and is a taxonomy field.
+  if (!($field = field_info_field($field_name)) || $field['type'] !== 'taxonomy_term_reference') {
+    // Error string. The JavaScript handler will realize this is not JSON and
+    // will display it as debugging information.
+    print t('Taxonomy field @field_name not found.', array('@field_name' => $field_name));
+    exit;
+  }
 
   // The user enters a comma-separated list of tags. We only autocomplete the last tag.
   $tags_typed = drupal_explode_tags($tags_typed);
diff --git a/modules/taxonomy/taxonomy.test b/modules/taxonomy/taxonomy.test
index 9a89b9c..7bdd882 100644
--- a/modules/taxonomy/taxonomy.test
+++ b/modules/taxonomy/taxonomy.test
@@ -696,6 +696,14 @@ class TaxonomyTermTestCase extends TaxonomyWebTestCase {
     $input = substr($term_objects['term3']->name, 0, 3);
     $this->drupalGet('taxonomy/autocomplete/taxonomy_' . $this->vocabulary->machine_name . '/' . $input);
     $this->assertRaw('{"' . $term_objects['term3']->name . '":"' . $term_objects['term3']->name . '"}', t('Autocomplete returns term %term_name after typing the first 3 letters.', array('%term_name' => $term_objects['term3']->name)));
+
+    // Test taxonomy autocomplete with a nonexistent field.
+    $field_name = $this->randomName();
+    $tag = $this->randomName();
+    $message = t("Taxonomy field @field_name not found.", array('@field_name' => $field_name));
+    $this->assertFalse(field_info_field($field_name), t('Field %field_name does not exist.', array('%field_name' => $field_name)));
+    $this->drupalGet('taxonomy/autocomplete/' . $field_name . '/' . $tag);
+    $this->assertRaw($message, t('Autocomplete returns correct error message when the taxonomy field does not exist.'));
   }
 
   /**