diff --git a/utils/fpdoc/unitdiff.pp b/utils/fpdoc/unitdiff.pp
index d77c5d4db6..da638f32be 100644
--- a/utils/fpdoc/unitdiff.pp
+++ b/utils/fpdoc/unitdiff.pp
@@ -12,6 +12,8 @@
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 }
 
+{$mode objfpc}
+{$h+}
 
 program unitdiff;