diff --git a/external/book b/external/book
index 0d602dbbd390b95554fe6794d46f4a0c6c121179..9e9fa8e04c221a54cfa83f017bb507bddf428615 160000
--- a/external/book
+++ b/external/book
@@ -1 +1 @@
-Subproject commit 0d602dbbd390b95554fe6794d46f4a0c6c121179
+Subproject commit 9e9fa8e04c221a54cfa83f017bb507bddf428615