diff --git a/Doc/Makefile b/Doc/Makefile
index 6ce9a91..cb6008e 100644
--- a/Doc/Makefile
+++ b/Doc/Makefile
@@ -211,7 +211,7 @@
     lib/libsunaudio.tex lib/libfileinput.tex lib/libimaplib.tex \
     lib/libpoplib.tex lib/libcalendar.tex lib/libpopen2.tex \
     lib/libbisect.tex lib/libmimetypes.tex lib/libsmtplib.tex lib/libcmd.tex \
-    lib/libmultifile.tex
+    lib/libmultifile.tex lib/libthreading.tex
 
 # LaTeX source files for Macintosh Library Modules.
 MACLIBFILES = mac/mac.tex mac/libmac.tex mac/libctb.tex mac/libmacconsole.tex \