diff --git a/src/Uri.php b/src/Uri.php
index 8f4ea5892..08e24063a 100644
--- a/src/Uri.php
+++ b/src/Uri.php
@@ -24,7 +24,7 @@ class Uri implements UriInterface
     /**
      * Character classes defined in RFC-3986
      */
-    const CHAR_UNRESERVED = '\w\-\.~';
+    const CHAR_UNRESERVED = 'a-zA-Z0-9_\-\.~';
     const CHAR_GEN_DELIMS = ':\/\?#\[\]@';
     const CHAR_SUB_DELIMS = '!\$&\'\(\)\*\+,;=';
     const CHAR_RESERVED   = ':\/\?#\[\]@!\$&\'\(\)\*\+,;=';