diff --git a/PVE/API2/Qemu/Agent.pm b/PVE/API2/Qemu/Agent.pm
index 1981cad9..9a51ef73 100644
--- a/PVE/API2/Qemu/Agent.pm
+++ b/PVE/API2/Qemu/Agent.pm
@@ -280,6 +280,7 @@ __PACKAGE__->register_method({
 	    },
 	    'input-data' => {
 		type => 'string',
+		maxLength => 64 * 1024,
 		description => "Data to pass as 'input-data' to the guest. Usually treated as STDIN to 'command'.",
 		optional => 1,
 	    },
diff --git a/PVE/CLI/qm.pm b/PVE/CLI/qm.pm
index 94bfaf83..5e4f96f0 100755
--- a/PVE/CLI/qm.pm
+++ b/PVE/CLI/qm.pm
@@ -702,7 +702,7 @@ __PACKAGE__->register_method({
 	    },
 	    'pass-stdin' => {
 		type => 'boolean',
-		description => "When set, read STDIN until EOF and forward to guest agent via 'input-data' (usually treated as STDIN to process launched by guest agent).",
+		description => "When set, read STDIN until EOF and forward to guest agent via 'input-data' (usually treated as STDIN to process launched by guest agent). Allows maximal 1 MiB.",
 		optional => 1,
 		default => 0,
 	    },