diff --git a/protocol/protocol.tex b/protocol/protocol.tex
index 5eb93892..8a9f82e0 100644
--- a/protocol/protocol.tex
+++ b/protocol/protocol.tex
@@ -873,6 +873,7 @@ electronic commerce and payment, financial privacy, proof of work, zero knowledg
 \newcommand{\activationHeight}{\term{activation block height}}
 \newcommand{\activationHeights}{\terms{activation block height}}
 \newcommand{\genesisBlock}{\term{genesis block}}
+\newcommand{\medianTimePast}{\term{median-time-past}}
 \newcommand{\transaction}{\term{transaction}}
 \newcommand{\transactions}{\terms{transaction}}
 \newcommand{\Transaction}{\titleterm{Transaction}}
@@ -9032,6 +9033,11 @@ the consensus protocol.
 Let $\ThresholdBits$ be as defined in \crossref{diffadjustment}, and let $\PoWMedianBlockSpan$
 be the constant defined in \crossref{constants}.
 
+\defining{Define the \medianTimePast of a \block to be the median (as defined in \crossref{diffadjustment})
+of the $\nTimeField$ fields of the \emph{preceding} $\PoWMedianBlockSpan$ \blocks (or all
+preceding \blocks if there are fewer than $\PoWMedianBlockSpan$). The \medianTimePast of a
+\genesisBlock is not defined.}
+
 \vspace{2ex}
 \begin{consensusrules}
   \item The \blockVersionNumber{} \MUST be greater than or equal to $4$.
@@ -9039,8 +9045,11 @@ be the constant defined in \crossref{constants}.
         $\ThresholdBits(\BlockHeight)$.
   \item The \block{} \MUST pass the difficulty filter defined in \crossref{difficulty}.
   \item $\solution$ \MUST represent a \validEquihashSolution as defined in \crossref{equihash}.
-  \item $\nTimeField$ \MUST be strictly greater than the median time of the previous
-        $\PoWMedianBlockSpan$ \blocks.
+  \item For each \block other than the \genesisBlock, $\nTimeField$ \MUST be strictly greater
+        than the \medianTimePast of that \block.
+  \item For each \block at \blockHeight $2$ or greater on the production network, or \blockHeight
+        $653606$ or greater on the test network, $\nTimeField$ \MUST be less than or equal to
+        the \medianTimePast of that \block plus $90 \mult 60$ seconds.
   \item The size of a \block{} \MUST be less than or equal to $2000000$ bytes.
   \saplingonwarditem{$\hashFinalSaplingRoot$ \MUST be $\LEBStoOSPOf{256}{\rt}$ where
         $\rt$ is the \merkleRoot of the \Sapling{} \noteCommitmentTree for the final
@@ -9078,6 +9087,10 @@ rejected by this rule at a given point in time may later be accepted.
         the median of the timestamps of the past $\PoWMedianBlockSpan$ \blocks. The
         Bitcoin Developer Reference \cite{Bitcoin-Block} was previously in error on this point,
         but has now been corrected.
+  \item The rule limiting $\nTimeField$ to be no later than $90 \mult 60$ seconds after the
+        \medianTimePast is a retrospective consensus change, applied as a soft fork in
+        \zcashd v2.1.1-1. It had not been violated by any \block from the given \blockHeights
+        in the consensus \blockchains of either the production or test networks.
 \overwinter{
   \item There are no changes to the \blockVersionNumber or format for \Overwinter.
 }
@@ -10251,6 +10264,10 @@ Peter Newell's illustration of the Jubjub bird, from \cite{Carroll1902}.
 \historyentry{2020.1.0}{2020-02-06}
 
 \begin{itemize}
+    \item Specify a retrospective soft fork implemented in \zcashd v2.1.1-1 that
+          limits the $\nTimeField$ field of a \block relative to its \medianTimePast.
+    \item Correct the definition of \medianTimePast for the first $\PoWMedianBlockSpan$
+          \blocks in a \blockchain.
     \item Add acknowledgements to Henry de Valence, Deirdre Connolly, Chelsea Komlo,
           and Zancas Wilcox.
     \item Add an acknowledgement to Trail of Bits for their security audit.
@@ -13165,7 +13182,7 @@ the cost of batched verification is therefore
 \listtheorems{theorem,lemma}
 }
 
-
+\needspace{30ex}
 \phantompart{Index}{index}
 
 \begin{flushleft}