diff --git a/Cargo.toml b/Cargo.toml
index 9cac71fd..e8e2c76d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -36,7 +36,7 @@ aes = { version = "0.8.4", optional = true }
 ctr = { version = "0.9.2", optional = true }
 crypto-mac = { version = "0.11.1", optional = true }
 hmac = { version = "0.11.0", optional = true }
-sha2 = { version = "0.9.5", optional = true }
+sha2 = { version = "0.9.5", optional = true, features = ["asm"] }
 hkdf = { version = "0.11.0", optional = true }
 pbkdf2 = { version = "0.8.0", optional = true }
 rand = { version = "0.8.5", optional = true }
diff --git a/README.md b/README.md
index bc11b089..348a046c 100644
--- a/README.md
+++ b/README.md
@@ -15,6 +15,16 @@ Its main use is to be used as a full text search backend for Matrix clients.
 Seshat provides JavaScript bindings which can be found in the
 [seshat-node](seshat-node) subdir.
 
+### Building the native module (with hardware crypto)
+
+```sh
+cd seshat-node
+
+# N.B. aarch64 requires you to explicitly enable hardware AES via RUSTFLAGS
+# otherwise seshat uses 10-20x more CPU than it should.
+RUSTFLAGS="--cfg aes_armv8" npm run build-bundled
+```
+
 ## Usage
 
 There are two modes of operation for Seshat, adding live events as they