diff --git a/protocol/protocol.tex b/protocol/protocol.tex
index 4131a096..442e637a 100644
--- a/protocol/protocol.tex
+++ b/protocol/protocol.tex
@@ -9188,6 +9188,9 @@ each \spendDescription (\crossref{spendencoding}), and each \outputDescription (
   \item The semantics of \transactions with \transactionVersionNumber not equal to\sprout{
         either $1$ or $2$ is not currently defined. Miners \MUSTNOT create \blocks
         containing such \transactions.
+  \item The \transactionVersionNumber{} \hexint{7FFFFFFF}, and the \versionGroupID{} \hexint{FFFFFFFF},
+        are reserved for use in experimental extensions to \transaction format or semantics on private
+        testnets. They \MUSTNOT be used on the \Zcash \Mainnet or \Testnet.
 }\notsprout{
         $1$, $2$, \overwinter{$3$,}\sapling{ or $4$} is not currently defined.
         Miners \MUSTNOT create \blocks before the \Overwinter \activationHeight
@@ -10901,6 +10904,8 @@ Peter Newell's illustration of the Jubjub bird, from \cite{Carroll1902}.
           \end{itemize}
           \vspace{-1.5ex}
 } %sapling
+    \item Reserve \transactionVersionNumber{} \hexint{7FFFFFFF} and \versionGroupID{} \hexint{FFFFFFFF}
+          for experimental use.
     \item Remove a statement that the language consisting of key and address encoding
           possibilities is prefix-free. (The human-readable forms are prefix-free but the
           raw encodings are not; for example, the \rawEncoding of a \Sapling \spendingKey