diff --git a/public/lib/moodlelib.php b/public/lib/moodlelib.php
index b528e9543b0..820df57993f 100644
--- a/public/lib/moodlelib.php
+++ b/public/lib/moodlelib.php
@@ -912,7 +912,7 @@ function get_host_from_url($url) {
  * images, objects, etc.
  */
 function html_is_blank($string) {
-    return trim(strip_tags((string)$string, '<img><object><applet><input><select><textarea><hr>')) == '';
+    return trim(strip_tags((string)$string, '<img><object><applet><input><select><textarea><hr><iframe>')) == '';
 }
 
 /**
diff --git a/public/lib/tests/moodlelib_test.php b/public/lib/tests/moodlelib_test.php
index 080164dce6a..b395cee84d4 100644
--- a/public/lib/tests/moodlelib_test.php
+++ b/public/lib/tests/moodlelib_test.php
@@ -5481,6 +5481,7 @@ EOT;
         $this->assertEquals(true, html_is_blank('<p> </p>'));
         $this->assertEquals(false, html_is_blank('<p>.</p>'));
         $this->assertEquals(false, html_is_blank('<img src="#">'));
+        $this->assertEquals(false, html_is_blank('<iframe></iframe>'));
     }
 
     /**