diff --git a/make-includes/build_document_rules.make b/make-includes/build_document_rules.make
index c628a02..9bfb2fb 100755
--- a/make-includes/build_document_rules.make
+++ b/make-includes/build_document_rules.make
@@ -147,11 +147,14 @@
 ################################################################################
 #
 # Lists of files for cleaning up. Add to these (using +=) as necessary in
-# derived makefiles.
+# derived makefiles. Note that ALL_CLEAN_FILES comprises files that need
+# to be deleted _in addition_ to those listed in WEB_CLEAN_FILES and
+# PRINT_CLEAN_FILES (that is, it's the list of additional files for the
+# "clean" target, which depends on "web-clean" and "print-clean" anyway).
 #
 WEB_CLEAN_FILES:=$(DERIVED_WEB_FILES) *-web*.png
 PRINT_CLEAN_FILES:=$(DERIVED_PRINT_FILES) *-print*.png *.pdf
-ALL_CLEAN_FILES:=$(DERIVED_XML) $(WEB_CLEAN_FILES) $(PRINT_CLEAN_FILES)
+ALL_CLEAN_FILES:=$(DERIVED_XML)
 
 
 ################################################################################