diff --git a/rtl/objpas/fpwidestring.pp b/rtl/objpas/fpwidestring.pp
index 0e633b3e65..644de3c516 100644
--- a/rtl/objpas/fpwidestring.pp
+++ b/rtl/objpas/fpwidestring.pp
@@ -248,7 +248,7 @@ begin
   if (cp=CP_UTF8) then
     begin
       destLen:=UnicodeToUtf8(nil,High(SizeUInt),source,len);
-      SetLength(dest,destLen);
+      SetLength(dest,destLen-1);
       UnicodeToUtf8(@dest[1],destLen,source,len);
       SetCodePage(dest,cp,False);
       exit;