diff --git a/etc/inc/interfaces.inc b/etc/inc/interfaces.inc
index 8d4faf7..ab8cf9c 100644
--- a/etc/inc/interfaces.inc
+++ b/etc/inc/interfaces.inc
@@ -2884,14 +2884,31 @@ function interface_configure($interface = "wan", $reloadall = false, $linkupeven
 			break;
 	}
 
-	if (!empty($wancfg['mtu'])) {
-		pfSense_interface_mtu($realif, $wancfg['mtu']);
-	} else {
-		$mtu = get_interface_default_mtu(remove_numbers($realhwif));
-		if ($mtu != get_interface_mtu($realhwif))
-			pfSense_interface_mtu($realhwif, $mtu);
+	$mtu = get_interface_default_mtu(remove_numbers($realhwif));
+
+	if (preg_match('/_vlan[0-9]/', $wancfg['if'])) {
+		foreach ($config['interfaces'] as $ifdescr => $ifdata) {
+			if ($ifdata['if'] == $realhwif) {
+				if (!empty($ifdata['mtu']))
+					$mtu = $ifdata['mtu'];
+				break;
+			}
+		}
+	} else if (!empty($wancfg['mtu'])) {
+		$mtu = $wancfg['mtu'];
 	}
 
+	if ($mtu != get_interface_mtu($realhwif))
+		pfSense_interface_mtu($realhwif, $mtu);
+
+	/*
+	 * All vlans need to use the same mtu value as their parent.
+	 */
+	if (is_array($config['vlans']['vlan']))
+		foreach ($config['vlans']['vlan'] as $vlan)
+			if (($vlan['if'] == $realhwif) && (get_interface_mtu($vlan['vlanif']) != $mtu))
+				pfSense_interface_mtu($vlan['vlanif'], $mtu);
+
 	if(does_interface_exist($wancfg['if']))
 		interfaces_bring_up($wancfg['if']);
 
diff --git a/usr/local/www/interfaces.php b/usr/local/www/interfaces.php
index 5062b36..818091b 100755
--- a/usr/local/www/interfaces.php
+++ b/usr/local/www/interfaces.php
@@ -92,6 +92,14 @@ if ($if == "wan" && !$wancfg['descr'])
 else if ($if == "lan" && !$wancfg['descr'])
 	$wancfg['descr'] = "LAN";
 
+$parent_vlan_if = "";
+if (preg_match('/_vlan[0-9]/', $wancfg['if'])) {
+	$realhwif_array = get_parent_interface($wancfg['if']);
+	// Need code to handle MLPPP if we ever use $realhwif for MLPPP handling
+	$realhwif = $realhwif_array[0];
+	$parent_vlan_if = convert_real_interface_to_friendly_interface_name($realhwif);
+	$wancfg['mtu'] = '';
+}
 
 foreach ($a_ppps as $pppid => $ppp) {
 	if ($wancfg['if'] == $ppp['if'])
@@ -1384,10 +1392,18 @@ $types6 = array("none" => gettext("None"), "staticv6" => gettext("Static IPv6"),
 						<tr>
 							<td valign="top" class="vncell"><?=gettext("MTU"); ?></td>
 							<td class="vtable">
-								<input name="mtu" type="text" class="formfld unknown" id="mtu" size="8" value="<?=htmlspecialchars($pconfig['mtu']);?>">
+								<input name="mtu" type="text" class="formfld unknown" id="mtu" size="8" value="<?=htmlspecialchars($pconfig['mtu']);?>"
+									<?php if(!empty($parent_vlan_if)) print "disabled"; ?>>
 								<br>
-								<?=gettext("If you leave this field blank, the adapter's default MTU will " .
-								"be used. This is typically 1500 bytes but can vary in some circumstances."); ?>
+								<?php
+									if (empty($parent_vlan_if))
+										print gettext("If you leave this field blank, the adapter's default MTU will " .
+										"be used. This is typically 1500 bytes but can vary in some circumstances.");
+									else
+										print gettext("This interface is a VLAN and it needs to use same MTU set for " .
+										"its parent. You can change parent's MTU") . "<a href=\"interfaces.php?if={$parent_vlan_if}\"> " .
+										gettext("here") . ".</a>";
+								?>
 							</td>
 						</tr>
 						<tr>