diff --git a/lib/PhpParser/PrettyPrinterAbstract.php b/lib/PhpParser/PrettyPrinterAbstract.php
index 3e3f8258..658a1675 100644
--- a/lib/PhpParser/PrettyPrinterAbstract.php
+++ b/lib/PhpParser/PrettyPrinterAbstract.php
@@ -1249,7 +1249,7 @@ abstract class PrettyPrinterAbstract implements PrettyPrinter {
         }
 
         if ($this->phpVersion->allowsDelInIdentifiers()) {
-            $this->labelCharMap[0x7f] = true;
+            $this->labelCharMap["\x7f"] = true;
         }
     }