diff --git a/course/lib.php b/course/lib.php
index 670e6d2aea7..c59cd481c79 100644
--- a/course/lib.php
+++ b/course/lib.php
@@ -1328,6 +1328,10 @@ function course_create_sections_if_missing($courseorid, $sections) {
  *
  * Updates both tables {course_sections} and {course_modules}
  *
+ * Note: This function does not use modinfo PROVIDED that the section you are
+ * adding the module to already exists. If the section does not exist, it will
+ * build modinfo if necessary and create the section.
+ *
  * @param int|stdClass $courseorid course id or course object
  * @param int $cmid id of the module already existing in course_modules table
  * @param int $sectionnum relative number of the section (field course_sections.section)
@@ -1347,9 +1351,16 @@ function course_add_cm_to_section($courseorid, $cmid, $sectionnum, $beforemod =
     } else {
         $courseid = $courseorid;
     }
-    course_create_sections_if_missing($courseorid, $sectionnum);
     // Do not try to use modinfo here, there is no guarantee it is valid!
-    $section = $DB->get_record('course_sections', array('course'=>$courseid, 'section'=>$sectionnum), '*', MUST_EXIST);
+    $section = $DB->get_record('course_sections',
+            array('course' => $courseid, 'section' => $sectionnum), '*', IGNORE_MISSING);
+    if (!$section) {
+        // This function call requires modinfo.
+        course_create_sections_if_missing($courseorid, $sectionnum);
+        $section = $DB->get_record('course_sections',
+                array('course' => $courseid, 'section' => $sectionnum), '*', MUST_EXIST);
+    }
+
     $modarray = explode(",", trim($section->sequence));
     if (empty($section->sequence)) {
         $newsequence = "$cmid";
diff --git a/course/tests/courselib_test.php b/course/tests/courselib_test.php
index 50d191ccefc..8ae3910233c 100644
--- a/course/tests/courselib_test.php
+++ b/course/tests/courselib_test.php
@@ -639,6 +639,55 @@ class courselib_testcase extends advanced_testcase {
         $this->assertEquals(range(0, $course->numsections + 1), $sectionscreated);
     }
 
+    public function test_course_add_cm_to_section() {
+        global $DB;
+        $this->resetAfterTest(true);
+
+        // Create course with 1 section.
+        $course = $this->getDataGenerator()->create_course(
+                array('shortname' => 'GrowingCourse',
+                    'fullname' => 'Growing Course',
+                    'numsections' => 1),
+                array('createsections' => true));
+
+        // Trash modinfo.
+        rebuild_course_cache($course->id, true);
+
+        // Create some cms for testing.
+        $cmids = array();
+        for ($i=0; $i<4; $i++) {
+            $cmids[$i] = $DB->insert_record('course_modules', array('course' => $course->id));
+        }
+
+        // Add it to section that exists.
+        course_add_cm_to_section($course, $cmids[0], 1);
+
+        // Check it got added to sequence.
+        $sequence = $DB->get_field('course_sections', 'sequence', array('course' => $course->id, 'section' => 1));
+        $this->assertEquals($cmids[0], $sequence);
+
+        // Add a second, this time using courseid variant of parameters.
+        course_add_cm_to_section($course->id, $cmids[1], 1);
+        $sequence = $DB->get_field('course_sections', 'sequence', array('course' => $course->id, 'section' => 1));
+        $this->assertEquals($cmids[0] . ',' . $cmids[1], $sequence);
+
+        // Check modinfo was not rebuilt (important for performance if calling
+        // repeatedly).
+        $this->assertNull($DB->get_field('course', 'modinfo', array('id' => $course->id)));
+
+        // Add one to section that doesn't exist (this might rebuild modinfo).
+        course_add_cm_to_section($course, $cmids[2], 2);
+        $this->assertEquals(3, $DB->count_records('course_sections', array('course' => $course->id)));
+        $sequence = $DB->get_field('course_sections', 'sequence', array('course' => $course->id, 'section' => 2));
+        $this->assertEquals($cmids[2], $sequence);
+
+        // Add using the 'before' option.
+        course_add_cm_to_section($course, $cmids[3], 2, $cmids[2]);
+        $this->assertEquals(3, $DB->count_records('course_sections', array('course' => $course->id)));
+        $sequence = $DB->get_field('course_sections', 'sequence', array('course' => $course->id, 'section' => 2));
+        $this->assertEquals($cmids[3] . ',' . $cmids[2], $sequence);
+    }
+
     public function test_reorder_sections() {
         global $DB;
         $this->resetAfterTest(true);