diff --git a/utils/fpdoc/mkfpdoc.pp b/utils/fpdoc/mkfpdoc.pp
index efe519b553..57212bd2d1 100644
--- a/utils/fpdoc/mkfpdoc.pp
+++ b/utils/fpdoc/mkfpdoc.pp
@@ -105,7 +105,7 @@ begin
          AInputFile:=S;
          OSTarget:=FProject.Options.OSTarget;
          CPUTarget:=FProject.Options.CPUTarget;
-         FProcessedUnits.Add(AInputFile);
+         FProcessedUnits.Add(UN);
          end;
        Inc(I);
        end;