diff --git a/src/install.md b/src/install.md
index cf4aa4a..1d09629 100644
--- a/src/install.md
+++ b/src/install.md
@@ -30,6 +30,13 @@ Synit builds upon many existing technologies, but primarily relies on the follow
 
  - Make, a C compiler, and so on; standard Unix programming tools.
 
+ - <a id="binfmt"></a>For cross builds (e.g. the very common case of building for `aarch64` on
+   an `x86_64` host), `qemu` and its `binfmt` support. On Debian, `apt install binfmt-support
+   qemu-user-static`. (**NB.** Version `1:7.0+dfsg-7` of `qemu-user-static` has a bug (possibly
+   [this one](https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1014177)) which makes
+   Docker-based cross builds hang. *Downgrading* `qemu-user-static` to version
+   `1:5.2+dfsg-11+deb11u2` worked for me.)
+
  - Source code for Synit components (see below).
 
  - A standard PostmarketOS distribution for the target computer or mobile phone. If you don't
@@ -71,6 +78,10 @@ To build, type `make ARCH=`*\<architecture\>* in the root of your checkout, wher
  - `aarch64` (default), for e.g. Pinephone or Samsung Galaxy S7 deployment
  - `x86_64`, for e.g. `qemu-amd64` deployment
 
+If you see errors of the form "`exec /bin/sh: exec format error`" while building, say, the
+`aarch64` packages using an `x86_64` build host, you need to install qemu's binfmt support. See
+[above](#binfmt).
+
 The result of the build will be a collection of Alpine Linux `apk` packages in
 `packaging/target/packages/`*\<architecture\>*`/`. At the time of writing, these include