diff --git a/resources/autoload.php b/resources/autoload.php
index 7f262cdc..158db4bc 100644
--- a/resources/autoload.php
+++ b/resources/autoload.php
@@ -32,6 +32,7 @@
 require_once __DIR__ . "/lib/exceptions/EnsureException.php";
 require_once __DIR__ . "/lib/exceptions/EncodingUnknownException.php";
 require_once __DIR__ . "/lib/exceptions/EncodingConversionException.php";
+require_once __DIR__ . "/lib/exceptions/UnityHTTPDMessageNotFoundException.php";
 
 require_once __DIR__ . "/config.php";
 require __DIR__ . "/init.php";
diff --git a/resources/lib/UnityHTTPD.php b/resources/lib/UnityHTTPD.php
index bed4bb95..d1794369 100644
--- a/resources/lib/UnityHTTPD.php
+++ b/resources/lib/UnityHTTPD.php
@@ -4,6 +4,7 @@
 
 use UnityWebPortal\lib\exceptions\NoDieException;
 use UnityWebPortal\lib\exceptions\ArrayKeyException;
+use UnityWebPortal\lib\exceptions\UnityHTTPDMessageNotFoundException;
 use RuntimeException;
 
 enum UnityHTTPDMessageLevel: string
@@ -226,13 +227,22 @@ public static function errorHandler(int $severity, string $message, string $file
 
     public static function getPostData(string $key): mixed
     {
-        try {
-            return $_POST[$key];
-        } catch (ArrayKeyException $e) {
-            self::badRequest('failed to get $_POST data', $e, [
-                '$_POST' => $_POST,
-            ]);
+        if (!isset($_SERVER)) {
+            throw new RuntimeException('$_SERVER is unset');
+        }
+        if (!array_key_exists("REQUEST_METHOD", $_SERVER)) {
+            throw new RuntimeException('$_SERVER has no array key "REQUEST_METHOD"');
+        }
+        if ($_SERVER["REQUEST_METHOD"] !== "POST") {
+            self::badRequest('$_SERVER["REQUEST_METHOD"] != "POST"');
         }
+        if (!isset($_POST)) {
+            self::badRequest('$_POST is unset');
+        }
+        if (!array_key_exists($key, $_POST)) {
+            self::badRequest("\$_POST has no array key '$key'");
+        }
+        return $_POST[$key];
     }
 
     public static function getUploadedFileContents(
@@ -325,6 +335,43 @@ public static function getMessages()
 
     public static function clearMessages()
     {
+        self::ensureSessionMessagesSanity();
         $_SESSION["messages"] = [];
     }
+
+    private static function getMessageIndex(
+        UnityHTTPDMessageLevel $level,
+        string $title,
+        string $body,
+    ) {
+        $messages = self::getMessages();
+        $error_msg = sprintf(
+            "message(level='%s' title='%s' body='%s'), not found. found messages: %s",
+            $level->value,
+            $title,
+            $body,
+            jsonEncode($messages),
+        );
+        foreach ($messages as $i => $message) {
+            if ($title == $message[0] && $body == $message[1] && $level == $message[2]) {
+                return $i;
+            }
+        }
+        throw new UnityHTTPDMessageNotFoundException($error_msg);
+    }
+
+    /* returns the 1st message that matches or throws UnityHTTPDMessageNotFoundException */
+    public static function getMessage(UnityHTTPDMessageLevel $level, string $title, string $body)
+    {
+        $index = self::getMessageIndex($level, $title, $body);
+        return $_SESSION["messages"][$index];
+    }
+
+    /* deletes the 1st message that matches or throws UnityHTTPDMessageNotFoundException */
+    public static function deleteMessage(UnityHTTPDMessageLevel $level, string $title, string $body)
+    {
+        $index = self::getMessageIndex($level, $title, $body);
+        unset($_SESSION["messages"][$index]);
+        $_SESSION["messages"] = array_values($_SESSION["messages"]);
+    }
 }
diff --git a/resources/lib/exceptions/UnityHTTPDMessageNotFoundException.php b/resources/lib/exceptions/UnityHTTPDMessageNotFoundException.php
new file mode 100644
index 00000000..214fc5bb
--- /dev/null
+++ b/resources/lib/exceptions/UnityHTTPDMessageNotFoundException.php
@@ -0,0 +1,5 @@
+<?php
+
+namespace UnityWebPortal\lib\exceptions;
+
+class UnityHTTPDMessageNotFoundException extends \Exception {}
diff --git a/resources/templates/header.php b/resources/templates/header.php
index 2e466f85..bc055b1f 100644
--- a/resources/templates/header.php
+++ b/resources/templates/header.php
@@ -147,15 +147,32 @@
               <div class='message %s'>
                 <h3>%s</h3>
                 <p>%s</p>
-                <button onclick=\"this.parentElement.style.display='none';\">×</button>
+                <button
+                  onclick=\"
+                    this.parentElement.style.display='none';
+                    $.ajax({
+                        url: '/panel/ajax/delete_message.php',
+                        method: 'POST',
+                        data: {
+                          'level': '%s',
+                          'title': '%s',
+                          'body': '%s',
+                        }
+                    });
+                  \"
+                >
+                  ×
+                </button>
               </div>
             ",
             htmlspecialchars($level->value),
             htmlspecialchars($title),
-            htmlspecialchars($body)
+            htmlspecialchars($body),
+            htmlspecialchars($level->value),
+            htmlspecialchars($title),
+            htmlspecialchars($body),
         );
     }
-    UnityHTTPD::clearMessages();
     if (
         isset($_SESSION["is_admin"])
         && $_SESSION["is_admin"]
diff --git a/test/functional/DeleteMessageTest.php b/test/functional/DeleteMessageTest.php
new file mode 100644
index 00000000..133c19e9
--- /dev/null
+++ b/test/functional/DeleteMessageTest.php
@@ -0,0 +1,40 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+use UnityWebPortal\lib\UnityHTTPD;
+use UnityWebPortal\lib\UnityHTTPDMessageLevel;
+
+class DeleteMessageTest extends TestCase
+{
+    public function testDeleteMessage(): void
+    {
+        switchUser(...getBlankUser());
+        $initial = UnityHTTPD::getMessages();
+        $this->assertEmpty($initial);
+        UnityHTTPD::messageDebug("foo1", "bar1");
+        UnityHTTPD::messageDebug("foo2", "bar2");
+        UnityHTTPD::messageDebug("foo3", "bar3");
+        UnityHTTPD::messageError("foo", "bar");
+        UnityHTTPD::messageInfo("foo", "bar");
+        UnityHTTPD::messageSuccess("foo", "bar");
+        UnityHTTPD::messageWarning("foo", "bar");
+        try {
+            $before = array_map("jsonEncode", UnityHTTPD::getMessages());
+            http_post(
+                __DIR__ . "/../../webroot/panel/ajax/delete_message.php",
+                [
+                    "level" => "debug",
+                    "title" => "foo2",
+                    "body" => "bar2",
+                ],
+                enforce_PRG: false,
+            );
+            $after = array_map("jsonEncode", UnityHTTPD::getMessages());
+            $difference = array_diff($before, $after);
+            $message_expected_removed = ["foo2", "bar2", UnityHTTPDMessageLevel::DEBUG];
+            $this->assertEqualsCanonicalizing([jsonEncode($message_expected_removed)], $difference);
+        } finally {
+            UnityHTTPD::clearMessages();
+        }
+    }
+}
diff --git a/test/phpunit-bootstrap.php b/test/phpunit-bootstrap.php
index 3061f59f..1b231a6c 100644
--- a/test/phpunit-bootstrap.php
+++ b/test/phpunit-bootstrap.php
@@ -23,6 +23,7 @@
 require_once __DIR__ . "/../resources/lib/exceptions/EnsureException.php";
 require_once __DIR__ . "/../resources/lib/exceptions/EncodingUnknownException.php";
 require_once __DIR__ . "/../resources/lib/exceptions/EncodingConversionException.php";
+require_once __DIR__ . "/../resources/lib/exceptions/UnityHTTPDMessageNotFoundException.php";
 
 use UnityWebPortal\lib\UnityGroup;
 use UnityWebPortal\lib\UnityHTTPD;
@@ -96,7 +97,7 @@ function switchUser(
     ensure(!is_null($USER));
 }
 
-function http_post(string $phpfile, array $post_data): void
+function http_post(string $phpfile, array $post_data, bool $enforce_PRG = true): void
 {
     global $LDAP,
         $SQL,
@@ -126,8 +127,10 @@ function http_post(string $phpfile, array $post_data): void
         unset($_POST);
         $_SERVER = $_PREVIOUS_SERVER;
     }
-    // https://en.wikipedia.org/wiki/Post/Redirect/Get
-    ensure($post_did_redirect_or_die, "post did not redirect or die!");
+    if ($enforce_PRG) {
+        // https://en.wikipedia.org/wiki/Post/Redirect/Get
+        ensure($post_did_redirect_or_die, "post did not redirect or die!");
+    }
 }
 
 function http_get(string $phpfile, array $get_data = []): void
diff --git a/webroot/panel/ajax/delete_message.php b/webroot/panel/ajax/delete_message.php
new file mode 100644
index 00000000..23870636
--- /dev/null
+++ b/webroot/panel/ajax/delete_message.php
@@ -0,0 +1,12 @@
+<?php
+
+require_once __DIR__ . "/../../../resources/autoload.php";
+
+use UnityWebPortal\lib\UnityHTTPD;
+use UnityWebPortal\lib\UnityHTTPDMessageLevel;
+
+$level_str = UnityHTTPD::getPostData("level");
+$level = UnityHTTPDMessageLevel::from($level_str);
+$title = UnityHTTPD::getPostData("title");
+$body = UnityHTTPD::getPostData("body");
+UnityHTTPD::deleteMessage($level, $title, $body);