diff --git a/lib/tests/questionlib_test.php b/lib/tests/questionlib_test.php
index 2347fb646db..59a2bcbfc72 100644
--- a/lib/tests/questionlib_test.php
+++ b/lib/tests/questionlib_test.php
@@ -2157,8 +2157,13 @@ class core_questionlib_testcase extends advanced_testcase {
             ['id999', 'id1000'],
             ['0', '1'],
             ['-1', '-2'],
+            ['01', '02'],
+            ['09', '10'],
             ['1.0E+29', '1.0E+30'], // Idnumbers are strings, not floats.
             ['1.0E-29', '1.0E-30'], // By the way, this is not a sensible idnumber!
+            ['10.1', '10.2'],
+            ['10.9', '10.10'],
+
         ];
     }