diff --git a/doc/Makefile b/doc/Makefile
index b94140b20..5544976ed 100644
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -31,6 +31,7 @@ SGML  =	apple2.sgml	\
 	library.sgml    \
         lynx.sgml       \
         nes.sgml        \
+        pet.sgml        \
         plus4.sgml      \
         vic20.sgml