diff --git a/common.mk b/common.mk
index 73312a6d87..0ea360ce62 100644
--- a/common.mk
+++ b/common.mk
@@ -692,7 +692,7 @@ undocumented: PHONY main srcs-doc
 	$(Q) $(RDOC) --quiet -C $(RDOCFLAGS) "$(srcdir)" | \
 	sed -n \
 	-e '/^ *# in file /{' -e 's///;N;s/\n/: /p' -e '}' \
-	-e 's/^ *\(.*[^ ]\) *# in file \(.*\)/\2: \1/p'
+	-e 's/^ *\(.*[^ ]\) *# in file \(.*\)/\2: \1/p' | sort
 
 RDOCBENCHOUT=/tmp/rdocbench