diff --git a/classes/mailer.php b/classes/mailer.php
index 60b1ce4fd..a15c8546b 100644
--- a/classes/mailer.php
+++ b/classes/mailer.php
@@ -45,7 +45,14 @@ class Mailer {
 			++$hooks_tried;
 		}
 
-		$headers = [ "From: $from_combined", "Content-Type: text/plain; charset=UTF-8" ];
+		$headers = [ "From: $from_combined" ];
+
+		if ($message_html) {
+			$headers[] = "MIME-Version: 1.0";
+			$headers[] = "Content-Type: text/html; charset=UTF-8";
+		} else {
+			$headers[] = "Content-Type: text/plain; charset=UTF-8";
+		}
 
 		$rc = mail($to_combined, $subject, $message, implode("\r\n", array_merge($headers, $additional_headers)));