diff --git a/Cargo.lock b/Cargo.lock
index 25b2707e..1ff965e3 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -333,6 +333,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d2f6c7dbe95a6ed67ad9f18e57daf93a2f034c524b99fd2b76d18fdfeb6660aa"
 dependencies = [
  "hybrid-array",
+ "zeroize",
 ]
 
 [[package]]
@@ -1028,6 +1029,7 @@ dependencies = [
  "const-oid",
  "crypto-common 0.2.2",
  "ctutils",
+ "zeroize",
 ]
 
 [[package]]
@@ -1175,6 +1177,7 @@ dependencies = [
  "futures",
  "hex",
  "hkdf",
+ "hmac 0.13.0",
  "libc",
  "libm",
  "mdns-sd",
diff --git a/Cargo.toml b/Cargo.toml
index 58188ce8..ae71c12e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -22,8 +22,12 @@ profiling = []
 [dependencies]
 ratatui = "0.30"
 secp256k1 = { version = "0.30", features = ["rand", "global-context"] }
-sha2 = "0.11"
+# The `zeroize` features clear the SHA-256 and HMAC states on drop. `hmac`'s
+# feature only forwards to `digest`'s, which `sha2`'s also turns on; it is
+# listed so the HMAC inside `hkdf` keeps it if `sha2`'s ever stops doing so.
+sha2 = { version = "0.11", features = ["zeroize"] }
 hkdf = "0.13"
+hmac = { version = "0.13", features = ["zeroize"] }
 ring = "0.17"
 libm = "0.2"
 zeroize = { version = "1.9", features = ["zeroize_derive"] }
diff --git a/src/noise/tests.rs b/src/noise/tests.rs
index 4c5e86b3..d8adec46 100644
--- a/src/noise/tests.rs
+++ b/src/noise/tests.rs
@@ -915,3 +915,15 @@ fn test_xk_invalid_msg3_size() {
             .is_err()
     );
 }
+
+/// The `zeroize` features of `sha2` and `hmac` are on, so the SHA-256 state
+/// that hashes each Diffie-Hellman result, and the two SHA-256 cores inside
+/// the HMAC that HKDF runs on, are cleared when dropped. Without `sha2`'s
+/// feature this does not compile; `hmac`'s forwards to the same `digest`
+/// feature, so dropping it alone changes nothing while `sha2`'s is on.
+#[test]
+fn test_sha256_states_used_by_hashing_and_hkdf_are_cleared_on_drop() {
+    fn clears_on_drop<T: zeroize::ZeroizeOnDrop>() {}
+    clears_on_drop::<sha2::Sha256>();
+    clears_on_drop::<<sha2::Sha256 as hmac::EagerHash>::Core>();
+}