diff --git a/course/format/lib.php b/course/format/lib.php
index 6985ded929fe6..bae152427c60f 100644
--- a/course/format/lib.php
+++ b/course/format/lib.php
@@ -1074,6 +1074,11 @@ public function delete_section($section, $forcedeleteifnotempty = false) {
         $DB->delete_records('course_sections', array('id' => $section->id));
         rebuild_course_cache($course->id, true);
 
+        // Delete section summary files.
+        $context = \context_course::instance($course->id);
+        $fs = get_file_storage();
+        $fs->delete_area_files($context->id, 'course', 'section', $section->id);
+
         // Descrease 'numsections' if needed.
         if ($decreasenumsections) {
             $this->update_course_format_options(array('numsections' => $course->numsections - 1));
diff --git a/lib/db/upgrade.php b/lib/db/upgrade.php
index 6c160dfe845a2..972c42172afe0 100644
--- a/lib/db/upgrade.php
+++ b/lib/db/upgrade.php
@@ -2337,5 +2337,29 @@ function xmldb_main_upgrade($oldversion) {
         upgrade_main_savepoint(true, 2018051703.09);
     }
 
+    if ($oldversion < 2018051704.01) {
+
+        // Delete all files that have been used in sections, which are already deleted.
+        $sql = "SELECT DISTINCT f.itemid as sectionid, f.contextid
+                  FROM {files} f
+             LEFT JOIN {course_sections} s ON f.itemid = s.id
+                 WHERE f.component = :component AND f.filearea = :filearea AND s.id IS NULL ";
+
+        $params = [
+            'component' => 'course',
+            'filearea' => 'section'
+        ];
+
+        $stalefiles = $DB->get_recordset_sql($sql, $params);
+
+        $fs = get_file_storage();
+        foreach ($stalefiles as $stalefile) {
+            $fs->delete_area_files($stalefile->contextid, 'course', 'section', $stalefile->sectionid);
+        }
+        $stalefiles->close();
+
+        upgrade_main_savepoint(true, 2018051704.01);
+    }
+
     return true;
 }
diff --git a/version.php b/version.php
index 0ec22c969604c..14d9f21675d68 100644
--- a/version.php
+++ b/version.php
@@ -29,7 +29,7 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$version  = 2018051704.00;              // 20180517      = branching date YYYYMMDD - do not modify!
+$version  = 2018051704.01;              // 20180517      = branching date YYYYMMDD - do not modify!
                                         //         RR    = release increments - 00 in DEV branches.
                                         //           .XX = incremental changes.