diff --git a/module/VuFind/tests/unit-tests/src/VuFindTest/Solr/UtilsTest.php b/module/VuFind/tests/unit-tests/src/VuFindTest/Solr/UtilsTest.php
index 364477564e7117166a3ec32510c307975c8ad3e6..6eedf2d47e1448d0cdbc722c4b5011ef79e2765e 100644
--- a/module/VuFind/tests/unit-tests/src/VuFindTest/Solr/UtilsTest.php
+++ b/module/VuFind/tests/unit-tests/src/VuFindTest/Solr/UtilsTest.php
@@ -79,6 +79,8 @@ class UtilsTest extends \VuFindTest\Unit\TestCase
             '1947-3' => '1947-03-01',
             '1973-02-31' => '1973-02-01',       // illegal day
             '1973-31-31' => '1973-01-01',       // illegal month
+            '1964-zz' => '1964-01-01',
+            '1964-01-zz' => '1964-01-01',
         );
         
         foreach ($tests as $in => $out) {