diff --git a/external/book b/external/book
index ef2934505b87eeb516eed7d083900ec88a62fb20..64c82c575ff842eaf02c62e61ec6cce78ecc0f42 160000
--- a/external/book
+++ b/external/book
@@ -1 +1 @@
-Subproject commit ef2934505b87eeb516eed7d083900ec88a62fb20
+Subproject commit 64c82c575ff842eaf02c62e61ec6cce78ecc0f42