diff --git a/include/markdown.php b/include/markdown.php
index 90d671fe4..d2379e7ed 100644
--- a/include/markdown.php
+++ b/include/markdown.php
@@ -64,6 +64,12 @@ function markdown_to_bb($s, $use_zrl = false, $options = []) {
 	// Escaping the hash tags
 	$s = preg_replace('/\#([^\s\#])/','#$1',$s);
 
+	// Protect mentions from being mangled by the markdown parser
+	$s = preg_replace_callback(
+		'|@\{([^}]+)\}|',
+		fn ($matches) => '@{' . base64_encode($matches[1]) . '}',
+		$s);
+
 	$s = MarkdownExtra::defaultTransform($s);
 
 
@@ -76,6 +82,12 @@ function markdown_to_bb($s, $use_zrl = false, $options = []) {
 		$s = str_replace("\r","",$s);
 	}
 
+	// Restore mentions after markdown conversion
+	$s = preg_replace_callback(
+		'|@\{([^}]+)\}|',
+		fn ($matches) => '@{' . base64_decode($matches[1]) . '}',
+		$s);
+
 	$s = str_replace('#','#',$s);
 
 	$s = html2bbcode($s);
diff --git a/tests/unit/includes/MarkdownTest.php b/tests/unit/includes/MarkdownTest.php
index 55dbb4445..eec809174 100644
--- a/tests/unit/includes/MarkdownTest.php
+++ b/tests/unit/includes/MarkdownTest.php
@@ -114,6 +114,10 @@ class MarkdownTest extends UnitTestCase {
 				'This is a link https://example.com/some/path more info.',
 				'This is a link https://example.com/some/path more info.',
 			],
+			'mention with underscores is untouched' => [
+				'@{_test_@somesite.example} @{test_2_@othersite.example}',
+				'@{_test_@somesite.example} @{test_2_@othersite.example}',
+			],
 		];
 	}