diff --git a/entityreference.install b/entityreference.install
index cc7bce5..091498b 100644
--- a/entityreference.install
+++ b/entityreference.install
@@ -163,3 +163,18 @@ function entityreference_update_7002() {
     ));
   }
 }
+
+/**
+ * Remove duplicate rows in the taxonomy_index table.
+ */
+function entityreference_update_7003() {
+  $tx_schema = drupal_get_schema('taxonomy_index');
+  db_create_table('taxonomy_index_tmp', $tx_schema);
+  $select = db_select('taxonomy_index', 'tx');
+  $select->fields('tx');
+  $select->groupBy('tx.nid');
+  $select->groupBy('tx.tid');
+  db_insert('taxonomy_index_tmp')->from($select)->execute();
+  db_drop_table('taxonomy_index');
+  db_rename_table('taxonomy_index_tmp', 'taxonomy_index');
+}
diff --git a/plugins/behavior/EntityReferenceBehavior_TaxonomyIndex.class.php b/plugins/behavior/EntityReferenceBehavior_TaxonomyIndex.class.php
index 43ac693..075b54d 100644
--- a/plugins/behavior/EntityReferenceBehavior_TaxonomyIndex.class.php
+++ b/plugins/behavior/EntityReferenceBehavior_TaxonomyIndex.class.php
@@ -144,18 +144,20 @@ class EntityReferenceBehavior_TaxonomyIndex extends EntityReference_BehaviorHand
       // already inserted in taxonomy_build_node_index().
       $tid_all = array_diff($tid_all, $original_tid_all);
 
-      // Insert index entries for all the node's terms.
+      // Insert index entries for all the node's terms, preventing duplicates.
       if (!empty($tid_all)) {
-        $query = db_insert('taxonomy_index')->fields(array('nid', 'tid', 'sticky', 'created'));
         foreach ($tid_all as $tid) {
-          $query->values(array(
+          $row = array(
             'nid' => $node->nid,
             'tid' => $tid,
             'sticky' => $sticky,
             'created' => $node->created,
-          ));
+          );
+          $query = db_merge('taxonomy_index')
+            ->key($row)
+            ->fields($row);
+          $query->execute();
         }
-        $query->execute();
       }
     }
   }
diff --git a/tests/entityreference.taxonomy.test b/tests/entityreference.taxonomy.test
index 6e4afb7..94b3f56 100644
--- a/tests/entityreference.taxonomy.test
+++ b/tests/entityreference.taxonomy.test
@@ -112,4 +112,52 @@ class EntityReferenceTaxonomyTestCase extends DrupalWebTestCase {
     $this->assertFalse(taxonomy_select_nodes(1));
   }
 
+  /**
+   * Add a second ER field from node/article to taxonomy.
+   *
+   * This should not cause {taxonomy_index} to receive duplicate entries.
+   */
+  protected function setupForIndexDuplicates() {
+    // Create an entity reference field.
+    $field = array(
+      'entity_types' => array('node'),
+      'settings' => array(
+        'handler' => 'base',
+        'target_type' => 'taxonomy_term',
+        'handler_settings' => array(
+          'target_bundles' => array(),
+        ),
+      ),
+      'field_name' => 'field_entityreference_term2',
+      'type' => 'entityreference',
+    );
+    $field = field_create_field($field);
+    $instance = array(
+      'field_name' => 'field_entityreference_term2',
+      'bundle' => 'article',
+      'entity_type' => 'node',
+    );
+
+    // Enable the taxonomy-index behavior.
+    $instance['settings']['behaviors']['taxonomy-index']['status'] = TRUE;
+    field_create_instance($instance);
+  }
+
+  /**
+   * Make sure the index only contains one entry for a given node->term
+   * reference, even when multiple ER fields link from the node bundle to terms.
+   */
+  public function testIndexDuplicates() {
+    // Extra setup for this test: add another ER field on this content type.
+    $this->setupForIndexDuplicates();
+
+    // Assert node insert with reference to term in first field.
+    $tid = 1;
+    $settings = array();
+    $settings['type'] = 'article';
+    $settings['field_entityreference_term'][LANGUAGE_NONE][0]['target_id'] = $tid;
+    $node = $this->drupalCreateNode($settings);
+
+    $this->assertEqual(taxonomy_select_nodes($tid), array($node->nid));
+  }
 }