diff --git a/external/book b/external/book
index bc32e86418714ff52fa8b698862751b199e167c0..2a6af012ff3ace20556917634785f82deaba6d80 160000
--- a/external/book
+++ b/external/book
@@ -1 +1 @@
-Subproject commit bc32e86418714ff52fa8b698862751b199e167c0
+Subproject commit 2a6af012ff3ace20556917634785f82deaba6d80