diff --git a/doc/arm/Makefile.in b/doc/arm/Makefile.in
index 5bd7a69817..cdf51c62db 100644
--- a/doc/arm/Makefile.in
+++ b/doc/arm/Makefile.in
@@ -66,7 +66,7 @@ notes.txt: notes.html
 	${W3M} -dump -cols 75 -O ascii -T text/html < notes.html | \
 		sed 's/  *$$//' | \
 		sed -e :a -e '/^\n*$$/{$$d;N;};/\n$$/ba' | \
-		sed '/ [!#]$$/{N;s| \([!#]\)\(\n\s*\)\([0-9][0-9]*\)|\2\1\3|;};' > notes.txt
+		sed '/ [!#]$$/{N;s| \([!#]\)\(\n[[:space:]]*\)\([0-9][0-9]*\)|\2\1\3|;};' > notes.txt
 
 # use xmllint to process include
 Bv9ARM.html: Bv9ARM-book.xml ${NOTESXML} releaseinfo.xml pkgversion.xml noteversion.xml