diff --git a/NEWS b/NEWS
index 123e5e886..9690d84a0 100644
--- a/NEWS
+++ b/NEWS
@@ -1,6 +1,7 @@
 ver 0.23.17 (not yet released)
 * protocol
   - "albumart" tries to send larger chunks if available
+  - explicitly disallow "idle" and "noidle" in command lists
 * storage
   - nfs: require libnfs 4.0 or later
 * database
diff --git a/doc/protocol.rst b/doc/protocol.rst
index 6c105c3e2..2677f5f83 100644
--- a/doc/protocol.rst
+++ b/doc/protocol.rst
@@ -156,6 +156,9 @@ fails, no more commands are executed and the appropriate
 ``list_OK`` is returned for each
 successful command executed in the command list.
 
+Only synchronous commands can be used in command lists.  Commands that
+suspend execution (``idle`` and ``noidle``) are not allowed.
+
 Ranges
 ======
 
diff --git a/src/client/Process.cxx b/src/client/Process.cxx
index 041e339c7..69bd78862 100644
--- a/src/client/Process.cxx
+++ b/src/client/Process.cxx
@@ -52,6 +52,13 @@ Client::ProcessCommandList(bool list_ok,
 	return CommandResult::OK;
 }
 
+[[gnu::pure]]
+static bool
+IsAsyncCommmand(const char *line) noexcept
+{
+	return StringIsEqual(line, "idle") || StringIsEqual(line, "noidle");
+}
+
 CommandResult
 Client::ProcessLine(char *line) noexcept
 {
@@ -67,6 +74,13 @@ Client::ProcessLine(char *line) noexcept
 		return CommandResult::CLOSE;
 	}
 
+	if (cmd_list.IsActive() && IsAsyncCommmand(line)) {
+		FmtWarning(client_domain,
+			   "[{}] not possible in comand list: \"{}\"",
+			   num, line);
+		return CommandResult::CLOSE;
+	}
+
 	if (StringIsEqual(line, "noidle")) {
 		if (idle_waiting) {
 			/* send empty idle response and leave idle mode */