diff --git a/lightningd/jsonrpc.c b/lightningd/jsonrpc.c
index f4a4166f43f0..d8b099ee225f 100644
--- a/lightningd/jsonrpc.c
+++ b/lightningd/jsonrpc.c
@@ -527,6 +527,33 @@ static void json_command_malformed(struct json_connection *jcon,
 	json_stream_close(js, NULL);
 }
 
+void json_notify_fmt(struct command *cmd,
+		     enum log_level level,
+		     const char *fmt, ...)
+{
+	va_list ap;
+	struct json_stream *js;
+
+	if (!cmd->send_notifications)
+		return;
+
+	js = json_stream_raw_for_cmd(cmd);
+
+	va_start(ap, fmt);
+	json_object_start(js, NULL);
+	json_add_string(js, "jsonrpc", "2.0");
+	json_add_string(js, "method", "message");
+	json_object_start(js, "params");
+	json_add_string(js, "id", cmd->id);
+	json_add_string(js, "level", log_level_name(level));
+	json_add_string(js, "message", tal_vfmt(tmpctx, fmt, ap));
+	json_object_end(js);
+	json_object_end(js);
+
+	json_stream_double_cr(js);
+	json_stream_flush(js);
+}
+
 struct json_stream *json_stream_raw_for_cmd(struct command *cmd)
 {
 	struct json_stream *js;
diff --git a/lightningd/jsonrpc.h b/lightningd/jsonrpc.h
index da80d4ad95ce..b01a03046165 100644
--- a/lightningd/jsonrpc.h
+++ b/lightningd/jsonrpc.h
@@ -7,6 +7,7 @@
 #include <common/errcode.h>
 #include <common/json.h>
 #include <common/json_stream.h>
+#include <common/status_levels.h>
 #include <stdarg.h>
 
 struct jsonrpc;
@@ -154,6 +155,12 @@ static inline void fixme_ignore(const struct command_result *res)
 {
 }
 
+/* Notifier to the caller. */
+void json_notify_fmt(struct command *cmd,
+		     enum log_level level,
+		     const char *fmt, ...)
+	PRINTF_FMT(3, 4);
+
 /* FIXME: For the few cases where return value is indeterminate */
 struct command_result *command_its_complicated(const char *why);
 
diff --git a/lightningd/test/run-jsonrpc.c b/lightningd/test/run-jsonrpc.c
index 444401c08f2c..7bde86ac3ec0 100644
--- a/lightningd/test/run-jsonrpc.c
+++ b/lightningd/test/run-jsonrpc.c
@@ -50,6 +50,9 @@ void log_io(struct log *log UNNEEDED, enum log_level dir UNNEEDED,
 	    const char *comment UNNEEDED,
 	    const void *data UNNEEDED, size_t len UNNEEDED)
 { fprintf(stderr, "log_io called!\n"); abort(); }
+/* Generated stub for log_level_name */
+const char *log_level_name(enum log_level level UNNEEDED)
+{ fprintf(stderr, "log_level_name called!\n"); abort(); }
 /* Generated stub for memleak_remove_strmap_ */
 void memleak_remove_strmap_(struct htable *memtable UNNEEDED, const struct strmap *m UNNEEDED)
 { fprintf(stderr, "memleak_remove_strmap_ called!\n"); abort(); }