diff --git a/lib/filelib.php b/lib/filelib.php
index b5f3fd13ce0..60fcea88f7c 100644
--- a/lib/filelib.php
+++ b/lib/filelib.php
@@ -3706,7 +3706,8 @@ 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 $mockresponse;
             }
diff --git a/mod/lti/locallib.php b/mod/lti/locallib.php
index 7668e676631..b0e05eba707 100644
--- a/mod/lti/locallib.php
+++ b/mod/lti/locallib.php
@@ -4392,6 +4392,13 @@ function lti_load_cartridge($url, $map, $propertiesmap = array()) {
     $curl = new curl();
     $response = $curl->get($url);
 
+    // Got a completely empty response (real or error), cannot process this with
+    // DOMDocument::loadXML() because it errors with ValueError. So let's throw
+    // the moodle_exception before waiting to examine the errors later.
+    if (trim($response) === '') {
+        throw new moodle_exception('errorreadingfile', '', '', $url);
+    }
+
     // TODO MDL-46023 Replace this code with a call to the new library.
     $origerrors = libxml_use_internal_errors(true);
     $origentity = lti_libxml_disable_entity_loader(true);
diff --git a/mod/lti/tests/locallib_test.php b/mod/lti/tests/locallib_test.php
index 37791f3e1ca..02f1e9c1f84 100644
--- a/mod/lti/tests/locallib_test.php
+++ b/mod/lti/tests/locallib_test.php
@@ -1841,6 +1841,20 @@ MwIDAQAB
         ];
     }
 
+    /**
+     * 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.
      *