diff --git a/lightningd/Makefile b/lightningd/Makefile
index 57143ba17..1d1f37243 100644
--- a/lightningd/Makefile
+++ b/lightningd/Makefile
@@ -32,6 +32,7 @@ LIGHTNINGD_OLD_LIB_SRC :=			\
 LIGHTNINGD_OLD_LIB_OBJS := $(LIGHTNINGD_OLD_LIB_SRC:.c=.o)
 LIGHTNINGD_OLD_LIB_HEADERS := $(LIGHTNINGD_OLD_LIB_SRC:.c=.h)
 
+# FIXME: put in a library so we don't link all of them.
 LIGHTNINGD_LIB_SRC :=				\
 	lightningd/channel.c			\
 	lightningd/channel_config.c		\
@@ -41,6 +42,7 @@ LIGHTNINGD_LIB_SRC :=				\
 	lightningd/funding_tx.c			\
 	lightningd/htlc_tx.c			\
 	lightningd/key_derive.c			\
+	lightningd/peer_failed.c			\
 	lightningd/utxo.c
 
 LIGHTNINGD_LIB_OBJS := $(LIGHTNINGD_LIB_SRC:.c=.o)
diff --git a/lightningd/peer_failed.c b/lightningd/peer_failed.c
new file mode 100644
index 000000000..6d622bae7
--- /dev/null
+++ b/lightningd/peer_failed.c
@@ -0,0 +1,41 @@
+#include <ccan/tal/str/str.h>
+#include <fcntl.h>
+#include <lightningd/crypto_sync.h>
+#include <lightningd/peer_failed.h>
+#include <status.h>
+#include <stdarg.h>
+#include <unistd.h>
+#include <wire/gen_peer_wire.h>
+
+/* We only support one channel per peer anyway */
+void peer_failed(int peer_fd, struct crypto_state *cs,
+		 const struct channel_id *channel_id,
+		 u16 error_code, const char *fmt, ...)
+{
+	va_list ap;
+	const char *errmsg;
+	struct channel_id all_channels;
+	u8 *msg;
+
+	/* BOLT #1:
+	 *
+	 * A node sending `error` MUST fail the channel referred to by the
+	 * `channel-id`, or if `channel-id` is `0xFFFFFFFFFFFFFFFF` it MUST
+	 * fail all channels and MUST close the connection.
+	 */
+	if (!channel_id) {
+		memset(&all_channels, 0xFF, sizeof(all_channels));
+		channel_id = &all_channels;
+	}
+
+	va_start(ap, fmt);
+	errmsg = tal_vfmt(NULL, fmt, ap);
+	va_end(ap);
+	msg = towire_error(errmsg, channel_id, (const u8 *)errmsg);
+
+	/* This is only best-effort; don't block. */
+	fcntl(peer_fd, F_SETFL, fcntl(peer_fd, F_GETFL) | O_NONBLOCK);
+	sync_crypto_write(cs, peer_fd, msg);
+
+	status_failed(error_code, "%s", errmsg);
+}
diff --git a/lightningd/peer_failed.h b/lightningd/peer_failed.h
new file mode 100644
index 000000000..2449fd68d
--- /dev/null
+++ b/lightningd/peer_failed.h
@@ -0,0 +1,21 @@
+#ifndef LIGHTNING_LIGHTNINGD_PEER_FAILED_H
+#define LIGHTNING_LIGHTNINGD_PEER_FAILED_H
+#include "config.h"
+#include <ccan/compiler/compiler.h>
+#include <ccan/short_types/short_types.h>
+
+struct channel_id;
+
+/**
+ * peer_failed - Try sending error to peer, but exit with status.
+ * @peer_fd: file descriptor for peer.
+ * @cs: the peer's current crypto state.
+ * @channel_id: channel with error, or NULL for all.
+ * @error_code: error code as per status_failed
+ * @fmt: format as per status_failed
+ */
+void peer_failed(int peer_fd, struct crypto_state *cs,
+		const struct channel_id *channel_id,
+		u16 error_code, const char *fmt, ...)
+	PRINTF_FMT(5,6) NORETURN;
+#endif /* LIGHTNING_STATUS_H */