diff --git a/search/engine/solr/classes/engine.php b/search/engine/solr/classes/engine.php
index 74b2e08e7b1..f908d50ed79 100644
--- a/search/engine/solr/classes/engine.php
+++ b/search/engine/solr/classes/engine.php
@@ -272,7 +272,7 @@ class engine extends \core_search\engine {
 
         $query = new \SolrDisMaxQuery();
 
-        $this->set_query($query, $data->q);
+        $this->set_query($query, self::replace_underlines($data->q));
         $this->add_fields($query);
 
         // Search filters applied, we don't cache these filters as we don't want to pollute the cache with tmp filters
@@ -750,6 +750,23 @@ class engine extends \core_search\engine {
         return true;
     }
 
+    /**
+     * Replaces underlines at edges of words in the content with spaces.
+     *
+     * For example '_frogs_' will become 'frogs', '_frogs and toads_' will become 'frogs and toads',
+     * and 'frogs_and_toads' will be left as 'frogs_and_toads'.
+     *
+     * The reason for this is that for italic content_to_text puts _italic_ underlines at the start
+     * and end of the italicised phrase (not between words). Solr treats underlines as part of the
+     * word, which means that if you search for a word in italic then you can't find it.
+     *
+     * @param string $str String to replace
+     * @return string Replaced string
+     */
+    protected static function replace_underlines(string $str): string {
+        return preg_replace('~\b_|_\b~', '', $str);
+    }
+
     /**
      * Adds a text document to the search engine.
      *
@@ -758,6 +775,14 @@ class engine extends \core_search\engine {
      */
     protected function add_solr_document($doc) {
         $solrdoc = new \SolrInputDocument();
+
+        // Replace underlines in the content with spaces. The reason for this is that for italic
+        // text, content_to_text puts _italic_ underlines. Solr treats underlines as part of the
+        // word, which means that if you search for a word in italic then you can't find it.
+        if (array_key_exists('content', $doc)) {
+            $doc['content'] = self::replace_underlines($doc['content']);
+        }
+
         foreach ($doc as $field => $value) {
             $solrdoc->addField($field, $value);
         }
diff --git a/search/engine/solr/tests/engine_test.php b/search/engine/solr/tests/engine_test.php
index 372e9600b10..d501090bf15 100644
--- a/search/engine/solr/tests/engine_test.php
+++ b/search/engine/solr/tests/engine_test.php
@@ -1010,6 +1010,68 @@ class search_solr_engine_testcase extends advanced_testcase {
                 ['Post1', 'Post2'], $results);
     }
 
+    /**
+     * Tests searching for results containing words in italic text. (This used to fail.)
+     */
+    public function test_italics() {
+        global $USER;
+
+        // Use real search areas.
+        $this->search->clear_static();
+        $this->search->add_core_search_areas();
+
+        // Create a course and a forum.
+        $generator = $this->getDataGenerator();
+        $course = $generator->create_course();
+        $forum = $generator->create_module('forum', ['course' => $course->id]);
+
+        // As admin user, create forum discussions with various words in italics or with underlines.
+        $this->setAdminUser();
+        $forumgen = $generator->get_plugin_generator('mod_forum');
+        $forumgen->create_discussion(['course' => $course->id, 'forum' => $forum->id,
+                'userid' => $USER->id, 'name' => 'Post1',
+                'message' => '<p>This is a post about <i>frogs</i>.</p>']);
+        $forumgen->create_discussion(['course' => $course->id, 'forum' => $forum->id,
+                'userid' => $USER->id, 'name' => 'Post2',
+                'message' => '<p>This is a post about <i>toads and zombies</i>.</p>']);
+        $forumgen->create_discussion(['course' => $course->id, 'forum' => $forum->id,
+                'userid' => $USER->id, 'name' => 'Post3',
+                'message' => '<p>This is a post about toads_and_zombies.</p>']);
+        $forumgen->create_discussion(['course' => $course->id, 'forum' => $forum->id,
+                'userid' => $USER->id, 'name' => 'Post4',
+                'message' => '<p>This is a post about _leading and trailing_ underlines.</p>']);
+
+        // Index the data.
+        $this->search->index();
+
+        // Search for 'frogs' should find the post.
+        $querydata = new stdClass();
+        $querydata->q = 'frogs';
+        $results = $this->search->search($querydata);
+        $this->assert_result_titles(['Post1'], $results);
+
+        // Search for 'toads' or 'zombies' should find post 2 (and not 3)...
+        $querydata->q = 'toads';
+        $results = $this->search->search($querydata);
+        $this->assert_result_titles(['Post2'], $results);
+        $querydata->q = 'zombies';
+        $results = $this->search->search($querydata);
+        $this->assert_result_titles(['Post2'], $results);
+
+        // Search for 'toads_and_zombies' should find post 3.
+        $querydata->q = 'toads_and_zombies';
+        $results = $this->search->search($querydata);
+        $this->assert_result_titles(['Post3'], $results);
+
+        // Search for '_leading' or 'trailing_' should find post 4.
+        $querydata->q = '_leading';
+        $results = $this->search->search($querydata);
+        $this->assert_result_titles(['Post4'], $results);
+        $querydata->q = 'trailing_';
+        $results = $this->search->search($querydata);
+        $this->assert_result_titles(['Post4'], $results);
+    }
+
     /**
      * Asserts that the returned documents have the expected titles (regardless of order).
      *