diff --git a/lib/filelib.php b/lib/filelib.php
index a5294a9d81e..ca8506424d2 100644
--- a/lib/filelib.php
+++ b/lib/filelib.php
@@ -3712,7 +3712,8 @@ class curl {
         $this->reset_request_state_vars();
 
         if ((defined('PHPUNIT_TEST') && PHPUNIT_TEST)) {
-            if ($mockresponse = array_pop(self::$mockresponses)) {
+            $mockresponse = array_pop(self::$mockresponses);
+            if ($mockresponse !== null) {
                 $this->info = [ 'http_code' => 200 ];
                 return $mockresponse;
             }
diff --git a/mod/lti/tests/locallib_test.php b/mod/lti/tests/locallib_test.php
index bd639b17090..a9697fe9fb1 100644
--- a/mod/lti/tests/locallib_test.php
+++ b/mod/lti/tests/locallib_test.php
@@ -1945,6 +1945,20 @@ MwIDAQAB
         $this->assertEquals(16, $countwithproxyid); // 1 type, 15 proxies.
     }
 
+    /**
+     * Verify that empty curl responses lead to the proper moodle_exception, not to XML ValueError.
+     *
+     * @covers ::lti_load_cartridge()
+     */
+    public function test_empty_reponse_lti_load_cartridge() {
+        // Mock the curl response to empty string, this is hardly
+        // reproducible in real life (only Windows + GHA).
+        \curl::mock_response('');
+
+        $this->expectException(\moodle_exception::class);
+        lti_load_cartridge('http://example.com/mocked/empty/response', []);
+    }
+
     /**
      * Create an LTI Tool.
      *