diff --git a/lightningd/hsm_control.c b/lightningd/hsm_control.c
index 5d67e3bfa..b0c313d54 100644
--- a/lightningd/hsm_control.c
+++ b/lightningd/hsm_control.c
@@ -42,6 +42,24 @@ int hsm_get_client_fd(struct lightningd *ld,
 	return hsm_fd;
 }
 
+static unsigned int hsm_msg(struct subd *hsmd,
+			    const u8 *msg, const int *fds UNUSED)
+{
+	/* We only expect one thing from the HSM that's not a STATUS message */
+	struct pubkey client_id;
+	u8 *bad_msg;
+
+	if (!fromwire_hsmstatus_client_bad_request(tmpctx, msg, &client_id,
+						   &bad_msg))
+		fatal("Bad status message from hsmd: %s", tal_hex(tmpctx, msg));
+
+	/* This should, of course, never happen. */
+	log_broken(hsmd->log, "client %s sent bad hsm request %s",
+		   type_to_string(tmpctx, struct pubkey, &client_id),
+		   tal_hex(tmpctx, bad_msg));
+	return 0;
+}
+
 void hsm_init(struct lightningd *ld)
 {
 	u8 *msg;
@@ -51,7 +69,9 @@ void hsm_init(struct lightningd *ld)
 	if (socketpair(AF_LOCAL, SOCK_STREAM, 0, fds) != 0)
 		err(1, "Could not create hsm socketpair");
 
-	ld->hsm = new_global_subd(ld, "lightning_hsmd", NULL, NULL,
+	ld->hsm = new_global_subd(ld, "lightning_hsmd",
+				  hsm_client_wire_type_name,
+				  hsm_msg,
 				  take(&fds[1]), NULL);
 	if (!ld->hsm)
 		err(1, "Could not subd hsm");
diff --git a/lightningd/subd.c b/lightningd/subd.c
index 589f1a412..c6a667879 100644
--- a/lightningd/subd.c
+++ b/lightningd/subd.c
@@ -400,6 +400,8 @@ static struct io_plan *sd_msg_read(struct io_conn *conn, struct subd *sd)
 	struct subd_req *sr;
 	struct db *db = sd->ld->wallet->db;
 	struct io_plan *plan;
+	unsigned int i;
+	bool freed = false;
 
 	/* Everything we do, we wrap in a database transaction */
 	db_begin_transaction(db);
@@ -464,29 +466,25 @@ static struct io_plan *sd_msg_read(struct io_conn *conn, struct subd *sd)
 	}
 
 	log_debug(sd->log, "UPDATE %s", sd->msgname(type));
-	if (sd->msgcb) {
-		unsigned int i;
-		bool freed = false;
 
-		/* Might free sd (if returns negative); save/restore sd->conn */
-		sd->conn = NULL;
-		tal_add_destructor2(sd, mark_freed, &freed);
+	/* Might free sd (if returns negative); save/restore sd->conn */
+	sd->conn = NULL;
+	tal_add_destructor2(sd, mark_freed, &freed);
 
-		i = sd->msgcb(sd, sd->msg_in, sd->fds_in);
-		if (freed)
-			goto close;
-		tal_del_destructor2(sd, mark_freed, &freed);
+	i = sd->msgcb(sd, sd->msg_in, sd->fds_in);
+	if (freed)
+		goto close;
+	tal_del_destructor2(sd, mark_freed, &freed);
 
-		sd->conn = conn;
+	sd->conn = conn;
 
-		if (i != 0) {
-			/* Don't ask for fds twice! */
-			assert(!sd->fds_in);
-			/* Don't free msg_in: we go around again. */
-			tal_steal(sd, sd->msg_in);
-			plan = sd_collect_fds(conn, sd, i);
-			goto out;
-		}
+	if (i != 0) {
+		/* Don't ask for fds twice! */
+		assert(!sd->fds_in);
+		/* Don't free msg_in: we go around again. */
+		tal_steal(sd, sd->msg_in);
+		plan = sd_collect_fds(conn, sd, i);
+		goto out;
 	}
 
 next:
@@ -651,7 +649,9 @@ static struct subd *new_subd(struct lightningd *ld,
 	sd->must_not_exit = false;
 	sd->talks_to_peer = talks_to_peer;
 	sd->msgname = msgname;
+	assert(msgname);
 	sd->msgcb = msgcb;
+	assert(msgcb);
 	sd->errcb = errcb;
 	sd->billboardcb = billboardcb;
 	sd->fds_in = NULL;
diff --git a/lightningd/subd.h b/lightningd/subd.h
index 72e929eab..a0ea87a36 100644
--- a/lightningd/subd.h
+++ b/lightningd/subd.h
@@ -76,7 +76,7 @@ struct subd {
  * @ld: global state
  * @name: basename of daemon
  * @msgname: function to get name from messages
- * @msgcb: function to call (inside db transaction) when non-fatal message received (or NULL)
+ * @msgcb: function to call (inside db transaction) when non-fatal message received
  * @...: NULL-terminated list of pointers to  fds to hand as fd 3, 4...
  *	(can be take, if so, set to -1)
  *
diff --git a/tests/fixtures.py b/tests/fixtures.py
index a097e2498..b9a2e07a4 100644
--- a/tests/fixtures.py
+++ b/tests/fixtures.py
@@ -134,6 +134,11 @@ def node_factory(request, directory, test_name, bitcoind, executor):
         err_count += checkBadReestablish(node)
     check_errors(request, err_count, "{} nodes had bad reestablish")
 
+    for node in nf.nodes:
+        err_count += checkBadHSMRequest(node)
+    if err_count:
+        raise ValueError("{} nodes had bad hsm requests".format(err_count))
+
     if not ok:
         request.node.has_errors = True
         raise Exception("At least one lightning exited with unexpected non-zero return code")
@@ -201,6 +206,12 @@ def checkBadReestablish(node):
     return 0
 
 
+def checkBadHSMRequest(node):
+    if node.daemon.is_in_log('bad hsm request'):
+        return 1
+    return 0
+
+
 @pytest.fixture
 def executor():
     ex = futures.ThreadPoolExecutor(max_workers=20)