diff --git a/services/horizon/CHANGELOG.md b/services/horizon/CHANGELOG.md
index 94f1d79973..d4f4c83811 100644
--- a/services/horizon/CHANGELOG.md
+++ b/services/horizon/CHANGELOG.md
@@ -11,6 +11,8 @@ This is the final release after the [release candidate](v2.17.0-release-candidat
   * `min_account_sequence_age` when it's `"0"`, as this is the default value when the condition is not set
   * `preconditions.ledgerbounds.max_ledger` when it's set to 0 (this means that there is no upper bound)
 
+- Timebounds within the `preconditions` object are a string containing int64 UNIX timestamps in seconds rather than formatted date-times (which was a bug) ([4361](https://github.com/stellar/go/pull/4361)).
+
 ## V2.17.0 Release Candidate
 
 **Upgrading to this version from <= v2.8.3 will trigger a state rebuild. During this process (which will take at least 10 minutes), Horizon will not ingest new ledgers.**
diff --git a/services/horizon/internal/integration/transaction_preconditions_test.go b/services/horizon/internal/integration/transaction_preconditions_test.go
index 13f29c59d6..44a6baac82 100644
--- a/services/horizon/internal/integration/transaction_preconditions_test.go
+++ b/services/horizon/internal/integration/transaction_preconditions_test.go
@@ -119,13 +119,23 @@ func TestTransactionPreconditionsTimeBounds(t *testing.T) {
 
 	txHistory, err := itest.Client().TransactionDetail(tx.Hash)
 	assert.NoError(t, err)
-	historyMaxTime, err := time.Parse(time.RFC3339, txHistory.Preconditions.TimeBounds.MaxTime)
+
+	// Check that the deprecated string datetime fields match the new UNIX
+	// timestamp fields.
+	deprecatedHistoryMinTime, err := time.Parse(time.RFC3339, txHistory.ValidAfter)
+	assert.NoError(t, err)
+	deprecatedHistoryMaxTime, err := time.Parse(time.RFC3339, txHistory.ValidBefore)
+	assert.NoError(t, err)
+
+	historyMinTime, err := strconv.ParseInt(txHistory.Preconditions.TimeBounds.MinTime, 10, 64)
 	assert.NoError(t, err)
-	historyMinTime, err := time.Parse(time.RFC3339, txHistory.Preconditions.TimeBounds.MinTime)
+	historyMaxTime, err := strconv.ParseInt(txHistory.Preconditions.TimeBounds.MaxTime, 10, 64)
 	assert.NoError(t, err)
 
-	assert.Equal(t, historyMaxTime.UTC().Unix(), txParams.Preconditions.TimeBounds.MaxTime)
-	assert.Equal(t, historyMinTime.UTC().Unix(), txParams.Preconditions.TimeBounds.MinTime)
+	assert.Equal(t, historyMinTime, deprecatedHistoryMinTime.UTC().Unix())
+	assert.Equal(t, historyMaxTime, deprecatedHistoryMaxTime.UTC().Unix())
+	assert.Equal(t, historyMinTime, txParams.Preconditions.TimeBounds.MinTime)
+	assert.Equal(t, historyMaxTime, txParams.Preconditions.TimeBounds.MaxTime)
 }
 
 func TestTransactionPreconditionsExtraSigners(t *testing.T) {
diff --git a/services/horizon/internal/resourceadapter/transaction.go b/services/horizon/internal/resourceadapter/transaction.go
index a72f202d36..547f8f4b40 100644
--- a/services/horizon/internal/resourceadapter/transaction.go
+++ b/services/horizon/internal/resourceadapter/transaction.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/base64"
 	"fmt"
+	"strconv"
 	"time"
 
 	"github.com/guregu/null"
@@ -65,8 +66,8 @@ func PopulateTransaction(
 		dest.ValidAfter = timeString(row.TimeBounds.Lower)
 
 		dest.Preconditions.TimeBounds = &protocol.TransactionPreconditionsTimebounds{
-			MaxTime: timeString(row.TimeBounds.Upper),
-			MinTime: timeString(row.TimeBounds.Lower),
+			MaxTime: timestampString(row.TimeBounds.Upper),
+			MinTime: timestampString(row.TimeBounds.Lower),
 		}
 	}
 
@@ -158,3 +159,11 @@ func timeString(in null.Int) string {
 
 	return time.Unix(in.Int64, 0).UTC().Format(time.RFC3339)
 }
+
+func timestampString(in null.Int) string {
+	if !in.Valid {
+		return ""
+	}
+
+	return strconv.FormatInt(in.Int64, 10)
+}
diff --git a/services/horizon/internal/resourceadapter/transaction_test.go b/services/horizon/internal/resourceadapter/transaction_test.go
index 9168f2c3e5..77246ae681 100644
--- a/services/horizon/internal/resourceadapter/transaction_test.go
+++ b/services/horizon/internal/resourceadapter/transaction_test.go
@@ -195,8 +195,8 @@ func TestPopulateTransaction_Preconditions(t *testing.T) {
 	p := dest.Preconditions
 	assert.Equal(t, validAfter.Format(time.RFC3339), dest.ValidAfter)
 	assert.Equal(t, validBefore.Format(time.RFC3339), dest.ValidBefore)
-	assert.Equal(t, validAfter.Format(time.RFC3339), p.TimeBounds.MinTime)
-	assert.Equal(t, validBefore.Format(time.RFC3339), p.TimeBounds.MaxTime)
+	assert.Equal(t, fmt.Sprint(validAfter.Unix()), p.TimeBounds.MinTime)
+	assert.Equal(t, fmt.Sprint(validBefore.Unix()), p.TimeBounds.MaxTime)
 	assert.Equal(t, minLedger, p.LedgerBounds.MinLedger)
 	assert.Equal(t, maxLedger, p.LedgerBounds.MaxLedger)
 	assert.Equal(t, fmt.Sprint(minAccountSequence), p.MinAccountSequence)
@@ -289,8 +289,8 @@ func TestPopulateTransaction_PreconditionsV2(t *testing.T) {
 		assert.NoError(t, PopulateTransaction(ctx, row.TransactionHash, &dest, row))
 
 		gotTimebounds := dest.Preconditions.TimeBounds
-		assert.Equal(t, "1970-01-01T00:00:05Z", gotTimebounds.MinTime)
-		assert.Equal(t, "1970-01-01T00:00:10Z", gotTimebounds.MaxTime)
+		assert.Equal(t, "5", gotTimebounds.MinTime)
+		assert.Equal(t, "10", gotTimebounds.MaxTime)
 	}
 }