diff --git a/core/includes/common.inc b/core/includes/common.inc
index 4a8b1f0..7b1b11c 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -7173,17 +7173,22 @@ function drupal_explode_tags($tags) {
   // This regexp allows the following types of user input:
   // this, "somecompany, llc", "and ""this"" w,o.rks", foo bar
   $regexp = '%(?:^|,\ *)("(?>[^"]*)(?>""[^"]* )*"|(?: [^",]*))%x';
-  preg_match_all($regexp, $tags, $matches);
-  $typed_tags = array_unique($matches[1]);
+  preg_match_all($regexp, $tags, $matches, PREG_OFFSET_CAPTURE);
+  $typed_tags = array();
+
+  foreach ($matches[1] as $match) {
+    $typed_tags[$match[1]] = $match[0];
+  }
+  $typed_tags = array_unique($typed_tags);
 
   $tags = array();
-  foreach ($typed_tags as $tag) {
+  foreach ($typed_tags as $position => $tag) {
     // If a user has escaped a term (to demonstrate that it is a group,
     // or includes a comma or quote character), we remove the escape
     // formatting so to save the term into the database as the user intends.
     $tag = trim(str_replace('""', '"', preg_replace('/^"(.*)"$/', '\1', $tag)));
     if ($tag != "") {
-      $tags[] = $tag;
+      $tags[$position] = $tag;
     }
   }
 
diff --git a/core/misc/autocomplete.js b/core/misc/autocomplete.js
index 8b0dd72..20ce682 100644
--- a/core/misc/autocomplete.js
+++ b/core/misc/autocomplete.js
@@ -206,7 +206,7 @@ Drupal.jsAC.prototype.populatePopup = function () {
 
   // Do search.
   this.db.owner = this;
-  this.db.search(this.input.value);
+  this.db.search(this.input.value, $input.get(0).selectionStart);
 };
 
 /**
@@ -272,7 +272,7 @@ Drupal.ACDB = function (uri) {
 /**
  * Performs a cached and delayed search.
  */
-Drupal.ACDB.prototype.search = function (searchString) {
+Drupal.ACDB.prototype.search = function (searchString, cursorPosition) {
   var db = this;
   this.searchString = searchString;
 
@@ -299,7 +299,7 @@ Drupal.ACDB.prototype.search = function (searchString) {
     // encodeURIComponent to allow autocomplete search terms to contain slashes.
     $.ajax({
       type: 'GET',
-      url: db.uri + '/' + Drupal.encodePath(searchString),
+      url: db.uri + '/' + encodeURIComponent(searchString) + '/' + cursorPosition,
       dataType: 'json',
       success: function (matches) {
         if (typeof matches.status === 'undefined' || matches.status !== 0) {
diff --git a/core/modules/taxonomy/taxonomy.pages.inc b/core/modules/taxonomy/taxonomy.pages.inc
index c84a6bd..08b6db7 100644
--- a/core/modules/taxonomy/taxonomy.pages.inc
+++ b/core/modules/taxonomy/taxonomy.pages.inc
@@ -102,17 +102,16 @@ function taxonomy_term_feed(Term $term) {
  *   (optional) A comma-separated list of term names entered in the
  *   autocomplete form element. Only the last term is used for autocompletion.
  *   Defaults to '' (an empty string).
+ * @param $cursor_position
+ *   (optional) The current position of the cursor within the autocomplete
+ *   form element. Defaults to 0.
  *
  * @see taxonomy_menu()
  * @see taxonomy_field_widget_info()
  */
-function taxonomy_autocomplete($field_name, $tags_typed = '') {
+function taxonomy_autocomplete($field_name, $tags_typed = '', $cursor_position = 0) {
   // If the request has a '/' in the search text, then the menu system will have
   // split it into multiple arguments, recover the intended $tags_typed.
-  $args = func_get_args();
-  // Shift off the $field_name argument.
-  array_shift($args);
-  $tags_typed = implode('/', $args);
 
   // Make sure the field exists and is a taxonomy field.
   if (!($field = field_info_field($field_name)) || $field['type'] !== 'taxonomy_term_reference') {
@@ -122,12 +121,28 @@ function taxonomy_autocomplete($field_name, $tags_typed = '') {
     exit;
   }
 
-  // The user enters a comma-separated list of tags. We only autocomplete the last tag.
-  $tags_typed = drupal_explode_tags($tags_typed);
-  $tag_last = drupal_strtolower(array_pop($tags_typed));
+  // The user enters a comma-separated list of tags.
+  $tags_typed_array = drupal_explode_tags($tags_typed);
+  // Try to find the tag based on the current cursor position.
+  $tag_current = '';
+  $tag_positions = array_keys($tags_typed_array);
+  $tag_positions[] = drupal_strlen($tags_typed) + 1;
+  $position_last = -1;
+  foreach ($tag_positions as $position) {
+    if ($cursor_position >= $position_last && $cursor_position < $position) {
+      // Tag found on cursor position.
+      $tag_current = $tags_typed_array[$position_last];
+      break;
+    }
+    // Save position for later use.
+    $position_last = $position;
+  }
+  if (isset($tags_typed_array[$position_last])) {
+    $tags_typed_array[$position_last] = '';
+  }
 
   $matches = array();
-  if ($tag_last != '') {
+  if ($tag_current != '') {
 
     // Part of the criteria for the query come from the field's own settings.
     $vids = array();
@@ -141,28 +156,32 @@ function taxonomy_autocomplete($field_name, $tags_typed = '') {
     $query->addTag('term_access');
 
     // Do not select already entered terms.
-    if (!empty($tags_typed)) {
-      $query->condition('t.name', $tags_typed, 'NOT IN');
+    if (!empty($tags_typed_array)) {
+      $query->condition('t.name', $tags_typed_array, 'NOT IN');
     }
     // Select rows that match by term name.
     $tags_return = $query
       ->fields('t', array('tid', 'name'))
       ->condition('t.vid', $vids)
-      ->condition('t.name', '%' . db_like($tag_last) . '%', 'LIKE')
+      ->condition('t.name', '%' . db_like($tag_current) . '%', 'LIKE')
       ->range(0, 10)
       ->execute()
       ->fetchAllKeyed();
 
-    $prefix = count($tags_typed) ? drupal_implode_tags($tags_typed) . ', ' : '';
-
     $term_matches = array();
     foreach ($tags_return as $tid => $name) {
       $n = $name;
+
       // Term names containing commas or quotes must be wrapped in quotes.
       if (strpos($name, ',') !== FALSE || strpos($name, '"') !== FALSE) {
         $n = '"' . str_replace('"', '""', $name) . '"';
       }
-      $term_matches[$prefix . $n] = check_plain($name);
+
+      $tags_typed_array[$position_last] = $n;
+      $prefix = count($tags_typed_array) ? implode(', ', $tags_typed_array) : '';
+
+      $term_matches[$prefix] = check_plain($name);
+
     }
   }
 
diff --git a/core/modules/taxonomy/taxonomy.test b/core/modules/taxonomy/taxonomy.test
index 4a3db65..6171778 100644
--- a/core/modules/taxonomy/taxonomy.test
+++ b/core/modules/taxonomy/taxonomy.test
@@ -49,9 +49,9 @@ class TaxonomyWebTestCase extends WebTestBase {
   /**
    * Returns a new term with random properties in vocabulary $vid.
    */
-  function createTerm($vocabulary) {
+  function createTerm($vocabulary, $term_name = NULL) {
     $term = entity_create('taxonomy_term', array(
-      'name' => $this->randomName(),
+      'name' => !empty($term_name) ? $term_name : $this->randomName(),
       'description' => $this->randomName(),
       // Use the first available text format.
       'format' => db_query_range('SELECT format FROM {filter_format}', 0, 1)->fetchField(),
@@ -61,9 +61,7 @@ class TaxonomyWebTestCase extends WebTestBase {
     taxonomy_term_save($term);
     return $term;
   }
-
 }
-
 /**
  * Tests the taxonomy vocabulary interface.
  */
@@ -799,6 +797,40 @@ class TaxonomyTermTestCase extends TaxonomyWebTestCase {
   }
 
   /**
+   * Tests taxonomy term autocompletion functionality.
+   */
+  function testTaxonomyAutocomplete() {
+    $vocabulary = $this->createVocabulary();
+
+    // Create two taxonomy terms without commas.
+    $term1 = $this->createTerm($vocabulary);
+    $term2 = $this->createTerm($vocabulary);
+    // Create a taxonomy term that contains a comma.
+    $term3 = $this->createTerm($vocabulary, $this->randomName() . ', ' . $this->randomName());
+
+    // Test autocompletion of term 1.  The term is alphanumeric only, so
+    // there is no extra quoting.
+    $input = substr($term1->name, 0, 3);
+    $this->drupalGet('taxonomy/autocomplete/taxonomy_' . $vocabulary->machine_name . '/' . $input);
+    $this->assertRaw('{"' . $term1->name . '":"' . $term1->name . '"}', t('Autocomplete returns term %term_name after typing the first 3 letters.', array('%term_name' => $term1->name)));
+    // Test autocompletion of term 3.  The term contains a comma, so expect
+    // the key to be quoted.
+     $input = substr($term3->name, 0, 3);
+     $this->drupalGet('taxonomy/autocomplete/taxonomy_' . $vocabulary->machine_name . '/' . $input);
+    $this->assertRaw('{"\"' . $term3->name . '\"":"' . $term3->name . '"}', t('Autocomplete returns term %term_name after typing the first 3 letters.', array('%term_name' => $term3->name)));
+
+
+    // Test autocompletion at a specific cursor position.
+    $term1_name = substr($term1->name, 0, 3);
+    $input = drupal_implode_tags(array($term1_name, $term2->name));
+    // Retrieve the autocomplete callback results for the given input and set
+    // the cursor after the third character.
+    $this->drupalGet('taxonomy/autocomplete/taxonomy_' . $vocabulary->machine_name . '/' . $input . '/3');
+    // The first term should be completed and after the second term.
+    $this->assertRaw('{"' . drupal_implode_tags(array($term2->name, $term1->name)) . '":"' . $term1->name . '"}', t('Autocomplete returns term %term1_name after %term2_name.', array('%term1_name' => $term1->name, '%term2_name' => $term2->name)));
+  }
+
+  /**
    * Save, edit and delete a term using the user interface.
    */
   function testTermInterface() {