diff --git a/commands.js b/commands.js
index 3a20725356..0afe53b4e5 100644
--- a/commands.js
+++ b/commands.js
@@ -13,6 +13,8 @@
 
 var crypto = require('crypto');
 
+const MAX_REASON_LENGTH = 300;
+
 var commands = exports.commands = {
 
 	version: function(target, room, user) {
@@ -443,6 +445,9 @@ var commands = exports.commands = {
 		if (room.isPrivate && room.auth) {
 			return this.sendReply('You can\'t warn here: This is a privately-owned room not subject to global rules.');
 		}
+		if (target.length > MAX_REASON_LENGTH) {
+			return this.sendReply('The reason is too long. It cannot excede ' + MAX_REASON_LENGTH + ' characters.');
+		}
 		if (!this.can('warn', targetUser, room)) return false;
 
 		this.addModCommand(''+targetUser.name+' was warned by '+user.name+'.' + (target ? " (" + target + ")" : ""));
@@ -483,6 +488,9 @@ var commands = exports.commands = {
 		if (!targetUser) {
 			return this.sendReply('User '+this.targetUsername+' not found.');
 		}
+		if (target.length > MAX_REASON_LENGTH) {
+			return this.sendReply('The reason is too long. It cannot excede ' + MAX_REASON_LENGTH + ' characters.');
+		}
 		if (!this.can('mute', targetUser, room)) return false;
 		if (targetUser.mutedRooms[room.id] || targetUser.locked || !targetUser.connected) {
 			var problem = ' but was already '+(!targetUser.connected ? 'offline' : targetUser.locked ? 'locked' : 'muted');
@@ -510,6 +518,9 @@ var commands = exports.commands = {
 		if (!targetUser) {
 			return this.sendReply('User '+this.targetUsername+' not found.');
 		}
+		if (target.length > MAX_REASON_LENGTH) {
+			return this.sendReply('The reason is too long. It cannot excede ' + MAX_REASON_LENGTH + ' characters.');
+		}
 		if (!this.can('mute', targetUser, room)) return false;
 
 		if (((targetUser.mutedRooms[room.id] && (targetUser.muteDuration[room.id]||0) >= 50*60*1000) || targetUser.locked) && !target) {
@@ -554,6 +565,9 @@ var commands = exports.commands = {
 		if (!targetUser) {
 			return this.sendReply('User '+this.targetUser+' not found.');
 		}
+		if (target.length > MAX_REASON_LENGTH) {
+			return this.sendReply('The reason is too long. It cannot excede ' + MAX_REASON_LENGTH + ' characters.');
+		}
 		if (!user.can('lock', targetUser)) {
 			return this.sendReply('/lock - Access denied.');
 		}
@@ -598,6 +612,9 @@ var commands = exports.commands = {
 		if (!targetUser) {
 			return this.sendReply('User '+this.targetUsername+' not found.');
 		}
+		if (target.length > MAX_REASON_LENGTH) {
+			return this.sendReply('The reason is too long. It cannot excede ' + MAX_REASON_LENGTH + ' characters.');
+		}
 		if (!this.can('ban', targetUser)) return false;
 
 		if (Users.checkBanned(targetUser.latestIp) && !target && !targetUser.connected) {
@@ -679,6 +696,9 @@ var commands = exports.commands = {
 
 	modnote: function(target, room, user, connection, cmd) {
 		if (!target) return this.parse('/help note');
+		if (target.length > MAX_REASON_LENGTH) {
+			return this.sendReply('The note is too long. It cannot excede ' + MAX_REASON_LENGTH + ' characters.');
+		}
 		if (!this.can('mute')) return false;
 		return this.privateModCommand('(' + user.name + ' notes: ' + target + ')');
 	},