diff --git a/doc/Makefile b/doc/Makefile
index 0a72feed..5737afeb 100644
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -33,8 +33,12 @@ prog.sgml:
 %.txt: %.sgml
 	./sgml2txt $<
 
+progspell: prog.sgml
+	sed -f prog-spell.sed <prog.sgml >prog.spell
+	ispell prog.spell
+
 userdocs: bird.html bird.dvi bird.txt
 
 clean:
-	rm -f *.html *.tex *.dvi *.log *.ps *.txt *.aux *.toc
+	rm -f *.html *.tex *.dvi *.log *.ps *.txt *.aux *.toc *.spell
 	rm -f prog.sgml
diff --git a/doc/prog-spell.sed b/doc/prog-spell.sed
new file mode 100644
index 00000000..426a0332
--- /dev/null
+++ b/doc/prog-spell.sed
@@ -0,0 +1,13 @@
+s%<type>[^<]*</type>%%g
+s%<param>[^<]*</param>%%g
+s%<func>[^<]*</func>%%g
+s%<funcdef>[^<]*</funcdef>%%g
+s%<type/[^</]*/%%g
+s%<param/[^</]*/%%g
+s%<func/[^</]*/%%g
+s%<funcdef/[^</]*/%%g
+s%<struct/[^</]*/%%g
+s%<const/[^</]*/%%g
+s%<[^<>/ ]\+/%%g
+s%</\?[^<>/ ]*>%%g
+s%&[^;]*;%%g