diff --git a/vector-space.md b/vector-space.md
index 8782cff..b4c94f9 100644
--- a/vector-space.md
+++ b/vector-space.md
@@ -43,6 +43,10 @@ So the header now looks like this:
     | tag | vecp-pointer | size | mark | payload...  /
     +-----+--------------+------+------+------------+
 
+#### Alternative mark-bit strategy
+
+A thought which has recently occurred to me is that the mark bit could be the case bit of the least significant byte of the tag. So that if the tag read 'IMAG' (a raster image), for example, when marked it would read 'IMAg'. This saves having a separately allocated mark in the header, but retains debugging clarity.
+
 ## Tags
 
 I really don't at this point have any idea what sorts of things we'll want to store in vector space. This is a non-exhaustive list of things I can think of just now.