diff --git a/python/obitools3/format/header.pyx b/python/obitools3/format/header.pyx
index 002911f..edea724 100755
--- a/python/obitools3/format/header.pyx
+++ b/python/obitools3/format/header.pyx
@@ -65,6 +65,8 @@ cdef class HeaderFormat:
                     if type(value) == Column_line:
                         value = value.bytes()
                     else:
+                        if type(value) == tuple:
+                            value=list(value)
                         value = str2bytes(str(bytes2str_object(value))) # genius programming
                 if value is not None:
                     lines.append(k + b"=" + value + b";")