diff --git a/src/Plugin/search_api/processor/PorterStemmer.php b/src/Plugin/search_api/processor/PorterStemmer.php
new file mode 100644
index 0000000..d2ab8e2
--- /dev/null
+++ b/src/Plugin/search_api/processor/PorterStemmer.php
@@ -0,0 +1,783 @@
+<?php
+
+namespace Drupal\search_api\Plugin\search_api\processor;
+
+use Drupal\search_api\Processor\FieldsProcessorPluginBase;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Stem search words using the Porter 2 stemmer algorithm.
+ *
+ * @SearchApiProcessor(
+ *   id = "porterstemmer",
+ *   label = @Translation("Stemmer"),
+ *   description = @Translation("Stem search words using the Porter 2 stemmer algorithm."),
+ *   stages = {
+ *     "pre_index_save" = 0,
+ *     "preprocess_index" = -20,
+ *     "preprocess_query" = -20,
+ *   }
+ * )
+ */
+class PorterStemmer extends FieldsProcessorPluginBase {
+
+  /**
+   * Static cache for already generated stems.
+   *
+   * @var array
+   */
+  protected $stems = array();
+
+  /**
+   * An array of original=stem pairs.
+   *
+   * @var string[]
+   */
+  protected $exceptions;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function defaultConfiguration() {
+    return array(
+      'exceptions' => array(
+        'texan=texa',
+        'mexican=mexic',
+      ),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setConfiguration(array $configuration) {
+    parent::setConfiguration($configuration);
+    unset($this->exceptions);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
+    $form = parent::buildConfigurationForm($form, $form_state);
+
+    $args = array(
+      '!algorithm' => 'https://github.com/markfullmer/porter2',
+      '!exceptions' => 'https://github.com/markfullmer/porter2#user-content-custom-exclusions',
+    );
+
+    $exceptions = $this->getConfiguration()['exceptions'];
+    if (is_array($exceptions)) {
+      $default_value = implode("\n", $exceptions);
+    }
+    else {
+      $default_value = $exceptions;
+    }
+    $description = $this->t('If the <a href=":algorithm">algorithm</a> does not stem words in your dataset in the desired way, you can enter specific exception in the form of WORD=STEM, where "WORD" is the term entered and "STEM" is the resulting stem. List each exception on a separate line. <a href=":exceptions">More info about stopwords.</a>.', array(':exceptions' => $args['!exceptions'], ':algorithm' => $args['!algorithm']));
+
+    $form['exceptions'] = array(
+      '#type' => 'textarea',
+      '#title' => $this->t('Exceptions'),
+      '#description' => $description,
+      '#default_value' => $default_value,
+    );
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
+    // Convert our text input to an array.
+    $form_state->setValue('exceptions', array_filter(array_map('trim', explode("\n", $form_state->getValues()['exceptions'])), 'strlen'));
+
+    parent::submitConfigurationForm($form, $form_state);
+  }
+
+  /**
+   * Gets the exclusions for this processor.
+   *
+   * @return string[]
+   *    An array of original=stem pairs.
+   */
+  protected function getExceptions() {
+    if (!isset($this->exceptions)) {
+      foreach ($this->configuration['exceptions'] as $exception) {
+        $item = parse_ini_string($exception, TRUE);
+        $this->exceptions[key($item)] = $item[key($item)];
+      }
+      return is_array($this->exceptions) ? $this->exceptions : array();
+    }
+    return $this->exceptions;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function process(&$value) {
+    // Load custom exceptions.
+    $exceptions = $this->getExceptions();
+    $words = preg_split('/[^\p{L}\p{N}]+/u', $value, -1, PREG_SPLIT_DELIM_CAPTURE);
+    $stemmed = array();
+    foreach ($words as $i => $word) {
+      if ($i % 2 == 0 && strlen($word)) {
+        if (!isset($this->stems[$word])) {
+          $stem = new SearchApiPorter2($word, $exceptions);
+          $this->stems[$word] = $stem->stem();
+        }
+        $stemmed[] = $this->stems[$word];
+      }
+      else {
+        $stemmed[] = $word;
+      }
+    }
+    $value = implode('', $stemmed);
+  }
+
+}
+
+/**
+ * Implements the Porter2 stemming algorithm.
+ *
+ * @see https://github.com/markfullmer/porter2
+ */
+class SearchApiPorter2 {
+
+  /**
+   * The word being stemmed.
+   *
+   * @var string
+   */
+  protected $word;
+
+  /**
+   * The R1 of the word.
+   *
+   * @var int
+   *
+   * @see http://snowball.tartarus.org/texts/r1r2.html.
+   */
+  protected $r1;
+
+  /**
+   * The R2 of the word.
+   *
+   * @var int
+   *
+   * @see http://snowball.tartarus.org/texts/r1r2.html.
+   */
+  protected $r2;
+
+  /**
+   * List of exceptions to be used.
+   *
+   * @var string[]
+   */
+  protected $exceptions = array();
+
+  /**
+   * Constructs a SearchApiPorter2 object.
+   *
+   * @param string $word
+   *   The word to stem.
+   * @param string[] $custom_exceptions
+   *   (optional) A custom list of exceptions.
+   */
+  public function __construct($word, $custom_exceptions = array()) {
+    $this->word = $word;
+    $this->exceptions = $custom_exceptions + array(
+      'skis' => 'ski',
+      'skies' => 'sky',
+      'dying' => 'die',
+      'lying' => 'lie',
+      'tying' => 'tie',
+      'idly' => 'idl',
+      'gently' => 'gentl',
+      'ugly' => 'ugli',
+      'early' => 'earli',
+      'only' => 'onli',
+      'singly' => 'singl',
+      'sky' => 'sky',
+      'news' => 'news',
+      'howe' => 'howe',
+      'atlas' => 'atlas',
+      'cosmos' => 'cosmos',
+      'bias' => 'bias',
+      'andes' => 'andes',
+    );
+
+    // Set initial y, or y after a vowel, to Y.
+    $inc = 0;
+    while ($inc <= $this->length()) {
+      if (substr($this->word, $inc, 1) === 'y' && ($inc == 0 || $this->isVowel($inc - 1))) {
+        $this->word = substr_replace($this->word, 'Y', $inc, 1);
+
+      }
+      $inc++;
+    }
+    // Establish the regions R1 and R2. See function R().
+    $this->r1 = $this->R(1);
+    $this->r2 = $this->R(2);
+  }
+
+  /**
+   * Computes the stem of the word.
+   *
+   * @return string
+   *   The word's stem.
+   */
+  public function stem() {
+    // Ignore exceptions & words that are two letters or less.
+    if ($this->exceptions() || $this->length() <= 2) {
+      return strtolower($this->word);
+    }
+    else {
+      $this->step0();
+      $this->step1a();
+      $this->step1b();
+      $this->step1c();
+      $this->step2();
+      $this->step3();
+      $this->step4();
+      $this->step5();
+    }
+    return strtolower($this->word);
+  }
+
+  /**
+   * Determines whether the word is contained in our list of exceptions.
+   *
+   * If so, the $word property is changed to the stem listed in the exceptions.
+   *
+   * @return bool
+   *   TRUE if the word was an exception, FALSE otherwise.
+   */
+  protected function exceptions() {
+    if (isset($this->exceptions[$this->word])) {
+      $this->word = $this->exceptions[$this->word];
+      return TRUE;
+    }
+    return FALSE;
+  }
+
+  /**
+   * Searches for the longest among the "s" suffixes and removes it.
+   *
+   * Implements step 0 of the Porter2 algorithm.
+   */
+  protected function step0() {
+    $found = FALSE;
+    $checks = array("'s'", "'s", "'");
+    foreach ($checks as $check) {
+      if (!$found && $this->hasEnding($check)) {
+        $this->removeEnding($check);
+        $found = TRUE;
+      }
+    }
+  }
+
+  /**
+   * Handles various suffixes, of which the longest is replaced.
+   *
+   * Implements step 1a of the Porter2 algorithm.
+   */
+  protected function step1a() {
+    $found = FALSE;
+    if ($this->hasEnding('sses')) {
+      $this->removeEnding('sses');
+      $this->addEnding('ss');
+      $found = TRUE;
+    }
+    $checks = array('ied', 'ies');
+    foreach ($checks as $check) {
+      if (!$found && $this->hasEnding($check)) {
+        $length = $this->length();
+        $this->removeEnding($check);
+        if ($length > 4) {
+          $this->addEnding('i');
+        }
+        else {
+          $this->addEnding('ie');
+        }
+        $found = TRUE;
+      }
+    }
+    if ($this->hasEnding('us') || $this->hasEnding('ss')) {
+      $found = TRUE;
+    }
+    // Delete if preceding word part has a vowel not immediately before the s.
+    if (!$found && $this->hasEnding('s') && $this->containsVowel(substr($this->word, 0, -2))) {
+      $this->removeEnding('s');
+    }
+  }
+
+  /**
+   * Handles various suffixes, of which the longest is replaced.
+   *
+   * Implements step 1b of the Porter2 algorithm.
+   */
+  protected function step1b() {
+    $exceptions = array(
+      'inning',
+      'outing',
+      'canning',
+      'herring',
+      'earring',
+      'proceed',
+      'exceed',
+      'succeed',
+    );
+    if (in_array($this->word, $exceptions)) {
+      return;
+    }
+    $checks = array('eedly', 'eed');
+    foreach ($checks as $check) {
+      if ($this->hasEnding($check)) {
+        if ($this->r1 !== $this->length()) {
+          $this->removeEnding($check);
+          $this->addEnding('ee');
+        }
+        return;
+      }
+    }
+    $checks = array('ingly', 'edly', 'ing', 'ed');
+    $second_endings = array('at', 'bl', 'iz');
+    foreach ($checks as $check) {
+      // If the ending is present and the previous part contains a vowel.
+      if ($this->hasEnding($check) && $this->containsVowel(substr($this->word, 0, -strlen($check)))) {
+        $this->removeEnding($check);
+        foreach ($second_endings as $ending) {
+          if ($this->hasEnding($ending)) {
+            $this->addEnding('e');
+            return;
+          }
+        }
+        // If the word ends with a double, remove the last letter.
+        $found = $this->removeDoubles();
+        // If the word is short, add e (so hop -> hope).
+        if (!$found && ($this->isShort())) {
+          $this->addEnding('e');
+        }
+        return;
+      }
+    }
+  }
+
+  /**
+   * Replaces suffix y or Y with i if after non-vowel not @ word begin.
+   *
+   * Implements step 1c of the Porter2 algorithm.
+   */
+  protected function step1c() {
+    if (($this->hasEnding('y') || $this->hasEnding('Y')) && $this->length() > 2 && !($this->isVowel($this->length() - 2))) {
+      $this->removeEnding('y');
+      $this->addEnding('i');
+    }
+  }
+
+  /**
+   * Implements step 2 of the Porter2 algorithm.
+   */
+  protected function step2() {
+    $checks = array(
+      "ization" => "ize",
+      "iveness" => "ive",
+      "fulness" => "ful",
+      "ational" => "ate",
+      "ousness" => "ous",
+      "biliti" => "ble",
+      "tional" => "tion",
+      "lessli" => "less",
+      "fulli" => "ful",
+      "entli" => "ent",
+      "ation" => "ate",
+      "aliti" => "al",
+      "iviti" => "ive",
+      "ousli" => "ous",
+      "alism" => "al",
+      "abli" => "able",
+      "anci" => "ance",
+      "alli" => "al",
+      "izer" => "ize",
+      "enci" => "ence",
+      "ator" => "ate",
+      "bli" => "ble",
+      "ogi" => "og",
+    );
+    foreach ($checks as $find => $replace) {
+      if ($this->hasEnding($find)) {
+        if ($this->inR1($find)) {
+          $this->removeEnding($find);
+          $this->addEnding($replace);
+        }
+        return;
+      }
+    }
+    if ($this->hasEnding('li')) {
+      if ($this->length() > 4 && $this->validLi($this->charAt(-3))) {
+        $this->removeEnding('li');
+      }
+    }
+  }
+
+  /**
+   * Implements step 3 of the Porter2 algorithm.
+   */
+  protected function step3() {
+    $checks = array(
+      'ational' => 'ate',
+      'tional' => 'tion',
+      'alize' => 'al',
+      'icate' => 'ic',
+      'iciti' => 'ic',
+      'ical' => 'ic',
+      'ness' => '',
+      'ful' => '',
+    );
+    foreach ($checks as $find => $replace) {
+      if ($this->hasEnding($find)) {
+        if ($this->inR1($find)) {
+          $this->removeEnding($find);
+          $this->addEnding($replace);
+        }
+        return;
+      }
+    }
+    if ($this->hasEnding('ative')) {
+      if ($this->inR2('ative')) {
+        $this->removeEnding('ative');
+      }
+    }
+  }
+
+  /**
+   * Implements step 4 of the Porter2 algorithm.
+   */
+  protected function step4() {
+    $checks = array(
+      'ement',
+      'ment',
+      'ance',
+      'ence',
+      'able',
+      'ible',
+      'ant',
+      'ent',
+      'ion',
+      'ism',
+      'ate',
+      'iti',
+      'ous',
+      'ive',
+      'ize',
+      'al',
+      'er',
+      'ic',
+    );
+    foreach ($checks as $check) {
+      // Among the suffixes, if found and in R2, delete.
+      if ($this->hasEnding($check)) {
+        if ($this->inR2($check)) {
+          if ($check !== 'ion' || in_array($this->charAt(-4), array('s', 't'))) {
+            $this->removeEnding($check);
+          }
+        }
+        return;
+      }
+    }
+  }
+
+  /**
+   * Implements step 5 of the Porter2 algorithm.
+   */
+  protected function step5() {
+    if ($this->hasEnding('e')) {
+      // Delete if in R2, or in R1 and not preceded by a short syllable.
+      if ($this->inR2('e') || ($this->inR1('e') && !$this->isShortSyllable($this->length() - 3))) {
+        $this->removeEnding('e');
+      }
+      return;
+    }
+    if ($this->hasEnding('l')) {
+      // Delete if in R2 and preceded by l.
+      if ($this->inR2('l') && $this->charAt(-2) == 'l') {
+        $this->removeEnding('l');
+      }
+    }
+  }
+
+  /**
+   * Removes certain double consonants from the word's end.
+   *
+   * @return bool
+   *   TRUE if a match was found and removed, FALSE otherwise.
+   */
+  protected function removeDoubles() {
+    $found = FALSE;
+    $doubles = array('bb', 'dd', 'ff', 'gg', 'mm', 'nn', 'pp', 'rr', 'tt');
+    foreach ($doubles as $double) {
+      if (substr($this->word, -2) == $double) {
+        $this->word = substr($this->word, 0, -1);
+        $found = TRUE;
+        break;
+      }
+    }
+    return $found;
+  }
+
+  /**
+   * Checks whether a character is a vowel.
+   *
+   * @param int $position
+   *   The character's position.
+   * @param string|null $word
+   *   (optional) The word in which to check. Defaults to $this->word.
+   * @param string[] $additional
+   *   (optional) Additional characters that should count as vowels.
+   *
+   * @return bool
+   *   TRUE if the character is a vowel, FALSE otherwise.
+   */
+  protected function isVowel($position, $word = NULL, $additional = array()) {
+    if ($word === NULL) {
+      $word = $this->word;
+    }
+    $vowels = array_merge(array('a', 'e', 'i', 'o', 'u', 'y'), $additional);
+    return in_array($this->charAt($position, $word), $vowels);
+  }
+
+  /**
+   * Retrieves the character at the given position.
+   *
+   * @param int $position
+   *   The 0-based index of the character. If a negative number is given, the
+   *   position is counted from the end of the string.
+   * @param string|null $word
+   *   (optional) The word from which to retrieve the character. Defaults to
+   *   $this->word.
+   *
+   * @return string
+   *   The character at the given position, or an empty string if the given
+   *   position was illegal.
+   */
+  protected function charAt($position, $word = NULL) {
+    if ($word === NULL) {
+      $word = $this->word;
+    }
+    $length = strlen($word);
+    if (abs($position) >= $length) {
+      return '';
+    }
+    if ($position < 0) {
+      $position += $length;
+    }
+    return $word[$position];
+  }
+
+  /**
+   * Determines whether the word ends in a "vowel-consonant" suffix.
+   *
+   * Unless the word is only two characters long, it also checks that the
+   * third-last character is neither "w", "x" nor "Y".
+   *
+   * @param int|null $position
+   *   (optional) If given, do not check the end of the word, but the character
+   *   at the given position, and the next one.
+   *
+   * @return bool
+   *   TRUE if the word has the described suffix, FALSE otherwise.
+   */
+  protected function isShortSyllable($position = NULL) {
+    if ($position === NULL) {
+      $position = $this->length() - 2;
+    }
+    // A vowel at the beginning of the word followed by a non-vowel.
+    if ($position === 0) {
+      return $this->isVowel(0) && !$this->isVowel(1);
+    }
+    // Vowel followed by non-vowel other than w, x, Y and preceded by
+    // non-vowel.
+    $additional = array('w', 'x', 'Y');
+    return !$this->isVowel($position - 1) && $this->isVowel($position) && !$this->isVowel($position + 1, NULL, $additional);
+  }
+
+  /**
+   * Determines whether the word is short.
+   *
+   * A word is called short if it ends in a short syllable and if R1 is null.
+   *
+   * @return bool
+   *   TRUE if the word is short, FALSE otherwise.
+   */
+  protected function isShort() {
+    return $this->isShortSyllable() && $this->r1 == $this->length();
+  }
+
+  /**
+   * Determines the start of a certain "R" region.
+   *
+   * R is a region after the first non-vowel following a vowel, or end of word.
+   *
+   * @param int $type
+   *   (optional) 1 or 2. If 2, then calculate the R after the R1.
+   *
+   * @return int
+   *   The R position.
+   */
+  protected function R($type = 1) {
+    $inc = 1;
+    if ($type === 2) {
+      $inc = $this->r1;
+    }
+    elseif ($this->length() > 5) {
+      $prefix_5 = substr($this->word, 0, 5);
+      if ($prefix_5 === 'gener' || $prefix_5 === 'arsen') {
+        return 5;
+      }
+      if ($this->length() > 6 && substr($this->word, 0, 6) === 'commun') {
+        return 6;
+      }
+    }
+
+    while ($inc <= $this->length()) {
+      if (!$this->isVowel($inc) && $this->isVowel($inc - 1)) {
+        $position = $inc;
+        break;
+      }
+      $inc++;
+    }
+    if (!isset($position)) {
+      $position = $this->length();
+    }
+    else {
+      // We add one, as this is the position AFTER the first non-vowel.
+      $position++;
+    }
+    return $position;
+  }
+
+  /**
+   * Checks whether the given string is contained in R1.
+   *
+   * @param string $string
+   *   The string.
+   *
+   * @return bool
+   *   TRUE if the string is in R1, FALSE otherwise.
+   */
+  protected function inR1($string) {
+    $r1 = substr($this->word, $this->r1);
+    return strpos($r1, $string) !== FALSE;
+  }
+
+  /**
+   * Checks whether the given string is contained in R2.
+   *
+   * @param string $string
+   *   The string.
+   *
+   * @return bool
+   *   TRUE if the string is in R2, FALSE otherwise.
+   */
+  protected function inR2($string) {
+    $r2 = substr($this->word, $this->r2);
+    return strpos($r2, $string) !== FALSE;
+  }
+
+  /**
+   * Determines the string length of the current word.
+   *
+   * @return int
+   *   The string length of the current word.
+   */
+  protected function length() {
+    return strlen($this->word);
+  }
+
+  /**
+   * Checks whether the word ends with the given string.
+   *
+   * @param string $string
+   *   The string.
+   *
+   * @return bool
+   *   TRUE if the word ends with the given string, FALSE otherwise.
+   */
+  protected function hasEnding($string) {
+    $length = strlen($string);
+    if ($length > $this->length()) {
+      return FALSE;
+    }
+    return (substr_compare($this->word, $string, -1 * $length, $length) === 0);
+  }
+
+  /**
+   * Appends a given string to the current word.
+   *
+   * @param string $string
+   *   The ending to append.
+   */
+  protected function addEnding($string) {
+    $this->word = $this->word . $string;
+  }
+
+  /**
+   * Removes a given string from the end of the current word.
+   *
+   * Does not check whether the ending is actually there.
+   *
+   * @param string $string
+   *   The ending to remove.
+   */
+  protected function removeEnding($string) {
+    $this->word = substr($this->word, 0, -strlen($string));
+  }
+
+  /**
+   * Checks whether the given string contains a vowel.
+   *
+   * @param string $string
+   *   The string to check.
+   *
+   * @return bool
+   *   TRUE if the string contains a vowel, FALSE otherwise.
+   */
+  protected function containsVowel($string) {
+    $inc = 0;
+    $return = FALSE;
+    while ($inc < strlen($string)) {
+      if ($this->isVowel($inc, $string)) {
+        $return = TRUE;
+        break;
+      }
+      $inc++;
+    }
+    return $return;
+  }
+
+  /**
+   * Checks whether the given string is a valid -li prefix.
+   *
+   * @param string $string
+   *   The string to check.
+   *
+   * @return bool
+   *   TRUE if the given string is a valid -li prefix, FALSE otherwise.
+   */
+  protected function validLi($string) {
+    return in_array($string, array(
+      'c',
+      'd',
+      'e',
+      'g',
+      'h',
+      'k',
+      'm',
+      'n',
+      'r',
+      't',
+    ));
+  }
+
+}