diff --git a/Makefile.am b/Makefile.am
index 7aa762c96..4a4021cb6 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -109,7 +109,8 @@ sile-%.md: CHANGELOG.md
 update_libtexpdf:
 	$(GIT) diff-index --quiet --cached HEAD || exit 1 # die if anything already staged
 	$(GIT) submodule update --init --remote -- libtexpdf
-	$(GIT) add -- libtexpdf
+	$(GIT) submodule status -- libtexpdf | $(AWK) '{ print $$1 }' > libtexpdf.git-rev
+	$(GIT) add -- libtexpdf libtexpdf.git-rev
 	$(GIT) diff-index --quiet --cached HEAD || $(GIT) commit -m "chore(build): Pin latest libtexpdf library submodule"
 
 gh-pages: