diff --git a/ulo/isabelle-prepare.sh b/ulo/isabelle-prepare.sh
index eea1c207cd56f061b0eb16340365045b7a4d3756..94591094011382737d6c2886bd0b3f8c6c78c6b8 100755
--- a/ulo/isabelle-prepare.sh
+++ b/ulo/isabelle-prepare.sh
@@ -25,6 +25,6 @@ for file in $files; do
 
     # uncompress, fix iris, compress again
     unxz "$file"
-    sed -i 's/|/%7C/g' "$file"
+    sed -i 's/|/%7C/g' "$rdf_file"
     gzip "$rdf_file"
 done