diff --git a/README.md b/README.md
index a246b5f..51cd422 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,9 @@ which was in turn derived from the Raspbian project.
 **Note**: Raspberry Pi OS 32 bit images are based primarily on Raspbian, while
 Raspberry Pi OS 64 bit images are based primarily on Debian.
 
+**Note**: 32 bit images should be built from the `master` branch.
+64 bit images should be built from the `arm64` branch.
+
 ## Dependencies
 
 pi-gen runs on Debian-based operating systems released after 2017, and we