diff --git a/hostconfig/thinkpad-nixos/hm.nix b/hostconfig/thinkpad-nixos/hm.nix
index aee1490..3ea399e 100644
--- a/hostconfig/thinkpad-nixos/hm.nix
+++ b/hostconfig/thinkpad-nixos/hm.nix
@@ -151,6 +151,7 @@ in
         "message/rfc822" = "colorize";
         "text/html" = "html | colorize";
         "subject,~^\\[PATCH" = "delta";
+        "subject,~^\\[RFC" = "delta";
       };
 
       openers = {