diff --git a/utils/fpdoc/fpdoc.pp b/utils/fpdoc/fpdoc.pp
index 122c55e81e..d1ffa734c4 100644
--- a/utils/fpdoc/fpdoc.pp
+++ b/utils/fpdoc/fpdoc.pp
@@ -18,6 +18,11 @@
 program FPDoc;
 
 uses
+{$ifdef LZX_USETHREADS}
+ {$ifdef Unix}
+   CThreads,
+ {$endif}
+{$endif}
 {$ifdef unix}
   cwstring,
 {$endif}