diff --git a/rtl/inc/ustrings.inc b/rtl/inc/ustrings.inc
index 6497ec0a04..908920de4f 100644
--- a/rtl/inc/ustrings.inc
+++ b/rtl/inc/ustrings.inc
@@ -18,6 +18,7 @@
 
 
 {$ifndef FPC_UNICODESTRING_TYPE_DEFINED}
+{$define FPC_UNICODESTRING_TYPE_DEFINED}
 {
   This file contains the implementation of the UnicodeString type,
   and all things that are needed for it.