diff --git a/make-includes/build_lecture_rules.make b/make-includes/build_lecture_rules.make
index f9b792e..ee2de8c 100755
--- a/make-includes/build_lecture_rules.make
+++ b/make-includes/build_lecture_rules.make
@@ -39,7 +39,7 @@
 # PDF files exist. They will be caught by by the "clean" target though.
 #
 TIDY_FILES+=*.tmp *.out *.log *.nav *.toc *.snm *.head *.dvi \
-	slides-combined.pdf slides-notes.pdf $(IMGDIR)/*-crop.pdf
+	slides-combined.pdf slides-notes.pdf
 CLEAN_FILES+=*.aux *.pdf