Clarify the minimum size for a RAC file
diff --git a/doc/spec/rac-spec.md b/doc/spec/rac-spec.md
index e649235..a47bbf3 100644
--- a/doc/spec/rac-spec.md
+++ b/doc/spec/rac-spec.md
@@ -149,10 +149,9 @@
## File Structure
-A RAC file (the `CFile`) must be at least 4 bytes long, and start with the 3
+A RAC file (the `CFile`) must be at least 32 bytes long, and start with the 3
byte `Magic` (see below), so that no valid RAC file can also be e.g. a valid
-JPEG file. The fourth byte is examined in the process described by the "Root
-Node at the CFile Start" section, below.
+JPEG file.
The `CFile` contains a tree of `Node`s. Each `Node` is either a `Branch Node`
(pointing to between 1 and 255 child `Node`s) or a `Leaf Node`. There must be
