diff --git a/plugins/facetapi/adapter.inc b/plugins/facetapi/adapter.inc
index f6bfe0e..649831f 100644
--- a/plugins/facetapi/adapter.inc
+++ b/plugins/facetapi/adapter.inc
@@ -77,7 +77,7 @@ abstract class FacetapiAdapter {
   /**
    * Define the array key in the params that is used for filters.
    */
-  const FILTER_KEY = 'f';
+  protected $filterKey = 'f';
 
   /**
    * Constructor, sets searcher and type of content being indexed.
@@ -98,6 +98,13 @@ abstract class FacetapiAdapter {
   }
 
   /**
+   * Returns the filter key.
+   */
+  static public function getFilterKey() {
+    return $this->filterKey;
+  }
+
+  /**
    * Returns a boolean flagging whether $this->info['searcher'] executed a search.
    *
    * @return
@@ -134,8 +141,8 @@ abstract class FacetapiAdapter {
 
     // We never want to use 'q' or 'page' params.
     $this->params = drupal_get_query_parameters($params, array('q', 'page'));
-    if (!isset($this->params[self::FILTER_KEY])) {
-      $this->params[self::FILTER_KEY] = array();
+    if (!isset($this->params[$this->filterKey])) {
+      $this->params[$this->filterKey] = array();
     }
 
     // Processes active items, returns this class.
@@ -157,7 +164,7 @@ abstract class FacetapiAdapter {
     }
 
     // Extracts valid filters from query string.
-    foreach ($this->params[self::FILTER_KEY] as $pos => $filter) {
+    foreach ($this->params[$this->filterKey] as $pos => $filter) {
       // Bails if an object or array.
       if (!is_scalar($filter)) {
         continue;
@@ -505,7 +512,7 @@ abstract class FacetapiAdapter {
 
     // Initializes base breadcrumb query.
     $query = $this->params;
-    unset($query[self::FILTER_KEY]);
+    unset($query[$this->filterKey]);
 
     // Adds the current search to the query.
     if ($keys) {
@@ -516,7 +523,7 @@ abstract class FacetapiAdapter {
     // Adds filters to the breadcrumb trail.
     $last = end($active_items);
     foreach ($active_items as $item) {
-      $query[self::FILTER_KEY][] = $item['field alias'] . ':' . $item['value'];
+      $query[$this->filterKey][] = $item['field alias'] . ':' . $item['value'];
 
       // Replaces with the mapped value.
       $value = $this->getMappedValue($item['facets'][0], $item['value']);
@@ -614,7 +621,7 @@ abstract class FacetapiAdapter {
       // Initializes each facet's render array.
       foreach ($this->getEnabledFacets() as $facet) {
         $this->processors[$facet['name']] = new FacetapiFacetProcessor(
-          $this->getFacet($facet), self::FILTER_KEY
+          $this->getFacet($facet), $this->filterKey
         );
         $this->processors[$facet['name']]->process();
       }