diff --git a/InstallationGuideR2B1.md b/InstallationGuideR2B1.md
index 85a14245..5b9a54e7 100644
--- a/InstallationGuideR2B1.md
+++ b/InstallationGuideR2B1.md
@@ -79,6 +79,8 @@ Known Issues
     qvm-create-default-dvm --default-template --default-script
     ```
 
+-   Qubes installer/system won't boot from a USB3-attached disks due to missing modules in initramfs (\#691). Please use USB2 port/device instead for now.
+
 Getting Help
 ------------