diff --git a/book/external/sphinx-iframes b/book/external/sphinx-iframes
index b0fcde7..2bc21b6 160000
--- a/book/external/sphinx-iframes
+++ b/book/external/sphinx-iframes
@@ -1 +1 @@
-Subproject commit b0fcde7e8957babcbda79bf861f6c2e2885c0df4
+Subproject commit 2bc21b6174b8e7dbd15c862c219bd506e06f9d13