diff --git a/filter/glossary/filter.php b/filter/glossary/filter.php
index 5098d50327b..1f2591836a1 100644
--- a/filter/glossary/filter.php
+++ b/filter/glossary/filter.php
@@ -168,9 +168,8 @@ class filter_glossary extends moodle_text_filter {
 
         if (!empty($GLOSSARY_EXCLUDEENTRY)) {
             foreach ($conceptlist as $key => $filterobj) {
-                if (!is_object($filterobj)) {
-                    continue;
-                }
+                // The original concept object was stored here in when $filterobj was constructed in
+                // get_all_concepts(). Get it back out now so we can check to see if it is excluded.
                 $concept = $filterobj->replacementcallbackdata[0];
                 if (!$concept->category && $concept->id == $GLOSSARY_EXCLUDEENTRY) {
                     unset($conceptlist[$key]);
@@ -182,7 +181,7 @@ class filter_glossary extends moodle_text_filter {
             return $text;
         }
 
-        return filter_phrases($text, $conceptlist);   // Actually search for concepts!
+        return filter_phrases($text, $conceptlist, null, null, false, true);
     }
 
     /**
diff --git a/filter/upgrade.txt b/filter/upgrade.txt
index ddfbd82c4bc..1dd24941a0a 100644
--- a/filter/upgrade.txt
+++ b/filter/upgrade.txt
@@ -1,6 +1,20 @@
 This file describes API changes in core filter API and plugins,
 information provided here is intended especially for developers.
 
+=== 3.6 ===
+
+* Although there is no API change that require you to update your filter,
+  if you use the filter_phrases() helper method, you may wish to take
+  advantage of the changes that were made in MDL-47962 to improve performance.
+
+  Now, instead of having to compute the replacement HTML for each phrase before
+  you construct the filterobject for it. You can instead pass a callback to
+  the filterobject constructor which is only called if the phrase is used.
+
+  To understand how to use this, see the comment on filterobject::__construct and
+  look at the filter_glossary changes as an example:
+  https://github.com/timhunt/moodle/commit/0b9220b527b1d70d2a2fad46c71f1cf2928f8759
+
 === 3.0 ===
 
 * New argument $skipfilters to filter_manager::filter_text to allow applying
diff --git a/lib/filterlib.php b/lib/filterlib.php
index 393fed0da71..d991075af96 100644
--- a/lib/filterlib.php
+++ b/lib/filterlib.php
@@ -1265,10 +1265,12 @@ function filter_context_may_have_filter_settings($context) {
  * @param array $ignoretagsopen   an array of opening tags that we should ignore while filtering
  * @param array $ignoretagsclose  an array of corresponding closing tags
  * @param bool $overridedefaultignore True to only use tags provided by arguments
+ * @param bool $linkarrayalreadyprepared True to say that filter_prepare_phrases_for_filtering
+ *      has already been called for $linkarray. Default false.
  * @return string
  */
 function filter_phrases($text, $linkarray, $ignoretagsopen = null, $ignoretagsclose = null,
-        $overridedefaultignore = false) {
+        $overridedefaultignore = false, $linkarrayalreadyprepared = false) {
 
     global $CFG;
 
@@ -1279,7 +1281,7 @@ function filter_phrases($text, $linkarray, $ignoretagsopen = null, $ignoretagscl
     $ignoretags = array();  // To store all the enclosig tags to be completely ignored.
     $tags = array();        // To store all the simple tags to be ignored.
 
-    if (!isset($linkarray['__preparedmarker'])) {
+    if (!$linkarrayalreadyprepared) {
         $linkarray = filter_prepare_phrases_for_filtering($linkarray);
     }
 
@@ -1326,11 +1328,9 @@ function filter_phrases($text, $linkarray, $ignoretagsopen = null, $ignoretagscl
 
     // Time to cycle through each phrase to be linked.
     foreach ($linkarray as $key => $linkobject) {
-        if ($key === '__preparedmarker') {
-            continue;
-        }
-
         if ($linkobject->workregexp === null) {
+            // This is the case if, when preparing the phrases for filtering,
+            // we decided that this was not a suitable phrase to match.
             continue;
         }
 
@@ -1429,8 +1429,6 @@ function filter_prepare_phrases_for_filtering(array $linkarray) {
         }
     }
 
-    $linkarray['__preparedmarker'] = 1;
-
     return $linkarray;
 }