diff --git a/data/conf/rspamd/custom/bad_header.map b/data/conf/rspamd/custom/bad_header.map
index b053f545..839c3c37 100644
--- a/data/conf/rspamd/custom/bad_header.map
+++ b/data/conf/rspamd/custom/bad_header.map
@@ -1 +1,2 @@
 /Thread-Topic:\s[a-zA-Z]{3}\s[a-zA-Z]{2}[\s\r\n]{0,1}[^a-zA-Z0-9][\r\n]/i
+/Thread-Topic:\s[a-zA-Z]{3}\s[a-zA-Z]{2}\s[a-zA-Z]{1}\s[a-zA-Z]{5}[\s\r\n]{0,1}[^a-zA-Z0-9][\r\n]/i