diff --git a/doc/.gitattributes b/doc/.gitattributes
index 689ad8bb1..7267b1213 100644
--- a/doc/.gitattributes
+++ b/doc/.gitattributes
@@ -12,3 +12,4 @@ fixes* NH_header=no
 * NH_filestag=(file%s_for_all_versions)
 Guidebook.tex	NH_DATESUB
 Guidebook.mn	NH_DATESUB
+*.6	NH_DATESUB