diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index 47fbf3cb54f..e8b79fe419b 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -10426,7 +10426,7 @@ class lang_string {
         // changes are not carried across.
         // To do this we always ensure $a or its properties/values are strings
         // and that any properties/values that arn't convertable are forgotten.
-        if (!empty($a)) {
+        if ($a !== null) {
             if (is_scalar($a)) {
                 $this->a = $a;
             } else if ($a instanceof lang_string) {
diff --git a/lib/tests/moodlelib_test.php b/lib/tests/moodlelib_test.php
index dbd3c74f9ac..31df330d70e 100644
--- a/lib/tests/moodlelib_test.php
+++ b/lib/tests/moodlelib_test.php
@@ -2168,6 +2168,11 @@ class core_moodlelib_testcase extends advanced_testcase {
         $this->assertInstanceOf('lang_string', $yes);
         $this->assertSame($yesexpected, (string)$yes);
 
+        // Test lazy loading (returning lang_string) correctly interpolates 0 being used as args.
+        $numdays = get_string('numdays', 'moodle', 0, true);
+        $this->assertInstanceOf(lang_string::class, $numdays);
+        $this->assertSame('0 days', (string) $numdays);
+
         // Test using a lang_string object as the $a argument for a normal
         // get_string call (returning string).
         $test = new lang_string('yes', null, null, true);