diff --git a/pkg/sql/as_of_test.go b/pkg/sql/as_of_test.go
index bf7fd5b8b02f..0941401ba4bc 100644
--- a/pkg/sql/as_of_test.go
+++ b/pkg/sql/as_of_test.go
@@ -122,11 +122,21 @@ func TestAsOfTime(t *testing.T) {
 		}
 	})
 
-	// Future queries shouldn't work.
+	// Future queries shouldn't work if not marked as synthetic.
 	if err := db.QueryRow("SELECT a FROM d.t AS OF SYSTEM TIME '2200-01-01'").Scan(&i); !testutils.IsError(err, "pq: AS OF SYSTEM TIME: cannot specify timestamp in the future") {
 		t.Fatal(err)
 	}
 
+	// Future queries shouldn't work if too far in the future.
+	if err := db.QueryRow("SELECT a FROM d.t AS OF SYSTEM TIME '+10h?'").Scan(&i); !testutils.IsError(err, "pq: request timestamp .* too far in future") {
+		t.Fatal(err)
+	}
+
+	// Future queries work if marked as synthetic and only slightly in future.
+	if err := db.QueryRow("SELECT a FROM d.t AS OF SYSTEM TIME '+10ms?'").Scan(&i); err != nil {
+		t.Fatal(err)
+	}
+
 	// Verify queries with positive scale work properly.
 	if _, err := db.Query("SELECT a FROM d.t AS OF SYSTEM TIME 1e1"); !testutils.IsError(err, `pq: relation "d.t" does not exist`) {
 		t.Fatal(err)
diff --git a/pkg/sql/catalog/lease/lease.go b/pkg/sql/catalog/lease/lease.go
index db40f7af8f1b..985a9e0155fb 100644
--- a/pkg/sql/catalog/lease/lease.go
+++ b/pkg/sql/catalog/lease/lease.go
@@ -400,7 +400,7 @@ func CountLeases(
 		)
 	}
 
-	stmt := fmt.Sprintf(`SELECT count(1) FROM system.public.lease AS OF SYSTEM TIME %s WHERE `,
+	stmt := fmt.Sprintf(`SELECT count(1) FROM system.public.lease AS OF SYSTEM TIME '%s' WHERE `,
 		at.AsOfSystemTime()) +
 		strings.Join(whereClauses, " OR ")
 	values, err := executor.QueryRowEx(
diff --git a/pkg/sql/exec_util.go b/pkg/sql/exec_util.go
index 2041b214ad47..e7c93de2741c 100644
--- a/pkg/sql/exec_util.go
+++ b/pkg/sql/exec_util.go
@@ -1222,7 +1222,7 @@ func (p *planner) EvalAsOfTimestamp(
 	if err != nil {
 		return hlc.Timestamp{}, err
 	}
-	if now := p.execCfg.Clock.Now(); now.Less(ts) {
+	if now := p.execCfg.Clock.Now(); now.Less(ts) && !ts.Synthetic {
 		return hlc.Timestamp{}, errors.Errorf(
 			"AS OF SYSTEM TIME: cannot specify timestamp in the future (%s > %s)", ts, now)
 	}
diff --git a/pkg/sql/sem/tree/BUILD.bazel b/pkg/sql/sem/tree/BUILD.bazel
index 06cd229f69ac..c2bd52d625af 100644
--- a/pkg/sql/sem/tree/BUILD.bazel
+++ b/pkg/sql/sem/tree/BUILD.bazel
@@ -105,6 +105,7 @@ go_library(
     visibility = ["//visibility:public"],
     deps = [
         "//pkg/base",
+        "//pkg/clusterversion",
         "//pkg/geo",
         "//pkg/geo/geopb",
         "//pkg/keys",
diff --git a/pkg/sql/sem/tree/as_of.go b/pkg/sql/sem/tree/as_of.go
index 6c2b6bb0550e..453b0ed8368f 100644
--- a/pkg/sql/sem/tree/as_of.go
+++ b/pkg/sql/sem/tree/as_of.go
@@ -17,6 +17,7 @@ import (
 	"time"
 
 	"github.com/cockroachdb/apd/v2"
+	"github.com/cockroachdb/cockroach/pkg/clusterversion"
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgcode"
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgerror"
 	"github.com/cockroachdb/cockroach/pkg/sql/sessiondata"
@@ -106,14 +107,24 @@ func DatumToHLC(evalCtx *EvalContext, stmtTimestamp time.Time, d Datum) (hlc.Tim
 	switch d := d.(type) {
 	case *DString:
 		s := string(*d)
+		// Parse synthetic flag.
+		syn := false
+		if strings.HasSuffix(s, "?") && evalCtx.Settings.Version.IsActive(evalCtx.Context, clusterversion.PriorReadSummaries) {
+			// NOTE: we don't parse this in mixed-version clusters because v20.2
+			// nodes will not know how to handle synthetic timestamps.
+			s = s[:len(s)-1]
+			syn = true
+		}
 		// Attempt to parse as timestamp.
 		if dt, _, err := ParseDTimestamp(evalCtx, s, time.Nanosecond); err == nil {
 			ts.WallTime = dt.Time.UnixNano()
+			ts.Synthetic = syn
 			break
 		}
 		// Attempt to parse as a decimal.
 		if dec, _, err := apd.NewFromString(s); err == nil {
 			ts, convErr = DecimalToHLC(dec)
+			ts.Synthetic = syn
 			break
 		}
 		// Attempt to parse as an interval.
@@ -122,6 +133,7 @@ func DatumToHLC(evalCtx *EvalContext, stmtTimestamp time.Time, d Datum) (hlc.Tim
 				convErr = errors.Errorf("interval value %v too small, absolute value must be >= %v", d, time.Microsecond)
 			}
 			ts.WallTime = duration.Add(stmtTimestamp, iv.Duration).UnixNano()
+			ts.Synthetic = syn
 			break
 		}
 		convErr = errors.Errorf("value is neither timestamp, decimal, nor interval")
diff --git a/pkg/util/hlc/timestamp.go b/pkg/util/hlc/timestamp.go
index af127a9c2457..550cab61b671 100644
--- a/pkg/util/hlc/timestamp.go
+++ b/pkg/util/hlc/timestamp.go
@@ -168,7 +168,11 @@ func ParseTimestamp(str string) (_ Timestamp, err error) {
 
 // AsOfSystemTime returns a string to be used in an AS OF SYSTEM TIME query.
 func (t Timestamp) AsOfSystemTime() string {
-	return fmt.Sprintf("%d.%010d", t.WallTime, t.Logical)
+	syn := ""
+	if t.Synthetic {
+		syn = "?"
+	}
+	return fmt.Sprintf("%d.%010d%s", t.WallTime, t.Logical, syn)
 }
 
 // IsEmpty retruns true if t is an empty Timestamp.
diff --git a/pkg/util/hlc/timestamp_test.go b/pkg/util/hlc/timestamp_test.go
index 4e4433874f58..8efc12f6a9aa 100644
--- a/pkg/util/hlc/timestamp_test.go
+++ b/pkg/util/hlc/timestamp_test.go
@@ -222,6 +222,9 @@ func TestAsOfSystemTime(t *testing.T) {
 		{makeTS(145, 0), "145.0000000000"},
 		{makeTS(145, 123), "145.0000000123"},
 		{makeTS(145, 1123456789), "145.1123456789"},
+		{makeSynTS(145, 0), "145.0000000000?"},
+		{makeSynTS(145, 123), "145.0000000123?"},
+		{makeSynTS(145, 1123456789), "145.1123456789?"},
 	}
 	for _, c := range testCases {
 		assert.Equal(t, c.exp, c.ts.AsOfSystemTime())