diff --git a/pkg/roachpb/data.go b/pkg/roachpb/data.go
index d82c45e76243..9e02e5b93784 100644
--- a/pkg/roachpb/data.go
+++ b/pkg/roachpb/data.go
@@ -934,8 +934,12 @@ func (t *Transaction) Restart(
 	// - the conflicting transaction's upgradePriority
 	t.UpgradePriority(MakePriority(userPriority))
 	t.UpgradePriority(upgradePriority)
-	t.WriteTooOld = false
+	// Reset all epoch-scoped state.
 	t.Sequence = 0
+	t.WriteTooOld = false
+	t.OrigTimestampWasObserved = false
+	t.IntentSpans = nil
+	t.InFlightWrites = nil
 }
 
 // BumpEpoch increments the transaction's epoch, allowing for an in-place
@@ -978,30 +982,68 @@ func (t *Transaction) Update(o *Transaction) {
 	if t.ID == (uuid.UUID{}) {
 		*t = *o
 		return
+	} else if t.ID != o.ID {
+		log.Fatalf(context.Background(), "updating txn %v with different txn %v", t, o)
+		return
 	}
 	if len(t.Key) == 0 {
 		t.Key = o.Key
 	}
-	if !t.Status.IsFinalized() {
-		if (t.Epoch < o.Epoch) || (t.Epoch == o.Epoch && o.Status != PENDING) {
-			t.Status = o.Status
-		}
-	}
 
-	// If the epoch or refreshed timestamp move forward, overwrite
-	// WriteTooOld, otherwise the flags are cumulative.
-	if t.Epoch < o.Epoch || t.RefreshedTimestamp.Less(o.RefreshedTimestamp) {
+	// Update epoch-scoped state, depending on the two transactions' epochs.
+	if t.Epoch < o.Epoch {
+		// Replace all epoch-scoped state.
+		t.Epoch = o.Epoch
+		t.Status = o.Status
 		t.WriteTooOld = o.WriteTooOld
 		t.OrigTimestampWasObserved = o.OrigTimestampWasObserved
-	} else {
-		t.WriteTooOld = t.WriteTooOld || o.WriteTooOld
-		t.OrigTimestampWasObserved = t.OrigTimestampWasObserved || o.OrigTimestampWasObserved
-	}
+		t.Sequence = o.Sequence
+		t.IntentSpans = o.IntentSpans
+		t.InFlightWrites = o.InFlightWrites
+	} else if t.Epoch == o.Epoch {
+		// Forward all epoch-scoped state.
+		switch t.Status {
+		case PENDING:
+			t.Status = o.Status
+		case STAGING:
+			if o.Status != PENDING {
+				t.Status = o.Status
+			}
+		case ABORTED:
+			if o.Status == COMMITTED {
+				log.Warningf(context.Background(), "updating ABORTED txn %v with COMMITTED txn %v", t, o)
+			}
+		case COMMITTED:
+			// Nothing to do.
+		}
 
-	if t.Epoch < o.Epoch {
-		t.Epoch = o.Epoch
+		// If the refreshed timestamp move forward, overwrite
+		// WriteTooOld, otherwise the flags are cumulative.
+		if t.RefreshedTimestamp.Less(o.RefreshedTimestamp) {
+			t.WriteTooOld = o.WriteTooOld
+			t.OrigTimestampWasObserved = o.OrigTimestampWasObserved
+		} else {
+			t.WriteTooOld = t.WriteTooOld || o.WriteTooOld
+			t.OrigTimestampWasObserved = t.OrigTimestampWasObserved || o.OrigTimestampWasObserved
+		}
+
+		if t.Sequence < o.Sequence {
+			t.Sequence = o.Sequence
+		}
+		if len(o.IntentSpans) > 0 {
+			t.IntentSpans = o.IntentSpans
+		}
+		if len(o.InFlightWrites) > 0 {
+			t.InFlightWrites = o.InFlightWrites
+		}
+	} else /* t.Epoch > o.Epoch */ {
+		// Ignore epoch-specific state from previous epoch.
+		if o.Status == COMMITTED {
+			log.Warningf(context.Background(), "updating txn %v with COMMITTED txn at earlier epoch %v", t, o)
+		}
 	}
 
+	// Forward each of the transaction timestamps.
 	t.Timestamp.Forward(o.Timestamp)
 	t.LastHeartbeat.Forward(o.LastHeartbeat)
 	t.OrigTimestamp.Forward(o.OrigTimestamp)
@@ -1026,17 +1068,9 @@ func (t *Transaction) Update(o *Transaction) {
 	for _, v := range o.ObservedTimestamps {
 		t.UpdateObservedTimestamp(v.NodeID, v.Timestamp)
 	}
-	t.UpgradePriority(o.Priority)
 
-	if t.Sequence < o.Sequence {
-		t.Sequence = o.Sequence
-	}
-	if len(o.IntentSpans) > 0 {
-		t.IntentSpans = o.IntentSpans
-	}
-	if len(o.InFlightWrites) > 0 {
-		t.InFlightWrites = o.InFlightWrites
-	}
+	// Ratchet the transaction priority.
+	t.UpgradePriority(o.Priority)
 }
 
 // UpgradePriority sets transaction priority to the maximum of current
diff --git a/pkg/roachpb/data_test.go b/pkg/roachpb/data_test.go
index d9de20337186..7b91cdce61e9 100644
--- a/pkg/roachpb/data_test.go
+++ b/pkg/roachpb/data_test.go
@@ -29,6 +29,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/util/encoding"
 	"github.com/cockroachdb/cockroach/pkg/util/hlc"
 	"github.com/cockroachdb/cockroach/pkg/util/leaktest"
+	"github.com/cockroachdb/cockroach/pkg/util/log"
 	"github.com/cockroachdb/cockroach/pkg/util/protoutil"
 	"github.com/cockroachdb/cockroach/pkg/util/randutil"
 	"github.com/cockroachdb/cockroach/pkg/util/uuid"
@@ -502,22 +503,74 @@ func TestTransactionUpdate(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	// Updating an empty Transaction copies all fields.
 	var txn2 Transaction
 	txn2.Update(&txn)
 
-	if err := zerofields.NoZeroField(txn2); err != nil {
-		t.Fatal(err)
-	}
+	expTxn2 := txn
+	require.Equal(t, expTxn2, txn2)
 
+	// Updating a Transaction at an earlier epoch replaces all epoch-scoped fields.
 	var txn3 Transaction
-	txn3.ID = uuid.MakeV4()
+	txn3.ID = txn.ID
+	txn3.Epoch = txn.Epoch - 1
+	txn3.Status = STAGING
 	txn3.Name = "carl"
 	txn3.Priority = 123
 	txn3.Update(&txn)
 
-	if err := zerofields.NoZeroField(txn3); err != nil {
-		t.Fatal(err)
-	}
+	expTxn3 := txn
+	expTxn3.Name = "carl"
+	require.Equal(t, expTxn3, txn3)
+
+	// Updating a Transaction at the same epoch forwards all epoch-scoped fields.
+	var txn4 Transaction
+	txn4.ID = txn.ID
+	txn4.Epoch = txn.Epoch
+	txn4.Status = STAGING
+	txn4.Sequence = txn.Sequence + 10
+	txn4.Name = "carl"
+	txn4.Priority = 123
+	txn4.Update(&txn)
+
+	expTxn4 := txn
+	expTxn4.Name = "carl"
+	expTxn4.Sequence = txn.Sequence + 10
+	require.Equal(t, expTxn4, txn4)
+
+	// Updating a Transaction at a future epoch ignores all epoch-scoped fields.
+	var txn5 Transaction
+	txn5.ID = txn.ID
+	txn5.Epoch = txn.Epoch + 1
+	txn5.Status = PENDING
+	txn5.Sequence = txn.Sequence - 10
+	txn5.Name = "carl"
+	txn5.Priority = 123
+	txn5.Update(&txn)
+
+	expTxn5 := txn
+	expTxn5.Name = "carl"
+	expTxn5.Epoch = txn.Epoch + 1
+	expTxn5.Status = PENDING
+	expTxn5.Sequence = txn.Sequence - 10
+	expTxn5.IntentSpans = nil
+	expTxn5.InFlightWrites = nil
+	expTxn5.WriteTooOld = false
+	expTxn5.OrigTimestampWasObserved = false
+	require.Equal(t, expTxn5, txn5)
+
+	// Updating a different transaction fatals.
+	var exited bool
+	log.SetExitFunc(true /* hideStack */, func(int) { exited = true })
+	defer log.ResetExitFunc()
+
+	var txn6 Transaction
+	txn6.ID = uuid.MakeV4()
+	origTxn6 := txn6
+	txn6.Update(&txn)
+
+	require.Equal(t, origTxn6, txn6)
+	require.True(t, exited)
 }
 
 func TestTransactionUpdateMinTimestamp(t *testing.T) {
@@ -611,6 +664,22 @@ func TestTransactionClone(t *testing.T) {
 	}
 }
 
+func TestTransactionRestart(t *testing.T) {
+	txn := nonZeroTxn
+	txn.Restart(1, 1, makeTS(25, 1))
+
+	expTxn := nonZeroTxn
+	expTxn.Epoch++
+	expTxn.Sequence = 0
+	expTxn.Timestamp = makeTS(25, 1)
+	expTxn.OrigTimestamp = makeTS(25, 1)
+	expTxn.WriteTooOld = false
+	expTxn.OrigTimestampWasObserved = false
+	expTxn.IntentSpans = nil
+	expTxn.InFlightWrites = nil
+	require.Equal(t, expTxn, txn)
+}
+
 // TestTransactionRecordRoundtrips tests a few properties about Transaction
 // and TransactionRecord protos. Remember that the latter is wire compatible
 // with the former and contains a subset of its protos.