diff -up ./src/JsonSchema/Uri/UriResolver.php.php8 ./src/JsonSchema/Uri/UriResolver.php
--- ./src/JsonSchema/Uri/UriResolver.php.php8	2021-03-31 14:05:54.880445272 +0200
+++ ./src/JsonSchema/Uri/UriResolver.php	2021-03-31 14:06:03.008417398 +0200
@@ -112,7 +112,7 @@ class UriResolver
         if ($relativePath == '') {
             return $basePath;
         }
-        if ($relativePath{0} == '/') {
+        if ($relativePath[0] == '/') {
             return $relativePath;
         }