diff --git a/encoding/jsonpb/decode_test.go b/encoding/jsonpb/decode_test.go
index cb99bcdc..9fb95d6d 100644
--- a/encoding/jsonpb/decode_test.go
+++ b/encoding/jsonpb/decode_test.go
@@ -1822,6 +1822,16 @@ func TestUnmarshal(t *testing.T) {
 		inputMessage: &knownpb.Duration{},
 		inputText:    `"0.5s"`,
 		wantMessage:  &knownpb.Duration{Nanos: 5e8},
+	}, {
+		desc:         "Duration max value",
+		inputMessage: &knownpb.Duration{},
+		inputText:    `"315576000000.999999999s"`,
+		wantMessage:  &knownpb.Duration{Seconds: 315576000000, Nanos: 999999999},
+	}, {
+		desc:         "Duration min value",
+		inputMessage: &knownpb.Duration{},
+		inputText:    `"-315576000000.999999999s"`,
+		wantMessage:  &knownpb.Duration{Seconds: -315576000000, Nanos: -999999999},
 	}, {
 		desc:         "Duration with +secs out of range",
 		inputMessage: &knownpb.Duration{},
@@ -1883,22 +1893,22 @@ func TestUnmarshal(t *testing.T) {
 		inputText:    `"2019-03-19T23:03:21.000000001Z"`,
 		wantMessage:  &knownpb.Timestamp{Seconds: 1553036601, Nanos: 1},
 	}, {
-		desc:         "Timestamp upper limit",
+		desc:         "Timestamp max value",
 		inputMessage: &knownpb.Timestamp{},
 		inputText:    `"9999-12-31T23:59:59.999999999Z"`,
 		wantMessage:  &knownpb.Timestamp{Seconds: 253402300799, Nanos: 999999999},
 	}, {
-		desc:         "Timestamp above upper limit",
+		desc:         "Timestamp above max value",
 		inputMessage: &knownpb.Timestamp{},
 		inputText:    `"9999-12-31T23:59:59-01:00"`,
 		wantErr:      true,
 	}, {
-		desc:         "Timestamp lower limit",
+		desc:         "Timestamp min value",
 		inputMessage: &knownpb.Timestamp{},
 		inputText:    `"0001-01-01T00:00:00Z"`,
 		wantMessage:  &knownpb.Timestamp{Seconds: -62135596800},
 	}, {
-		desc:         "Timestamp below lower limit",
+		desc:         "Timestamp below min value",
 		inputMessage: &knownpb.Timestamp{},
 		inputText:    `"0001-01-01T00:00:00+01:00"`,
 		wantErr:      true,
diff --git a/encoding/jsonpb/encode_test.go b/encoding/jsonpb/encode_test.go
index 0c128617..b0e39733 100644
--- a/encoding/jsonpb/encode_test.go
+++ b/encoding/jsonpb/encode_test.go
@@ -1421,6 +1421,14 @@ func TestMarshal(t *testing.T) {
 		desc:  "Duration with -secs -nanos",
 		input: &knownpb.Duration{Seconds: -123, Nanos: -450},
 		want:  `"-123.000000450s"`,
+	}, {
+		desc:  "Duration max value",
+		input: &knownpb.Duration{Seconds: 315576000000, Nanos: 999999999},
+		want:  `"315576000000.999999999s"`,
+	}, {
+		desc:  "Duration min value",
+		input: &knownpb.Duration{Seconds: -315576000000, Nanos: -999999999},
+		want:  `"-315576000000.999999999s"`,
 	}, {
 		desc:    "Duration with +secs -nanos",
 		input:   &knownpb.Duration{Seconds: 1, Nanos: -1},
@@ -1465,6 +1473,14 @@ func TestMarshal(t *testing.T) {
 		desc:  "Timestamp with 3-digit nanos",
 		input: &knownpb.Timestamp{Nanos: 1e7},
 		want:  `"1970-01-01T00:00:00.010Z"`,
+	}, {
+		desc:  "Timestamp max value",
+		input: &knownpb.Timestamp{Seconds: 253402300799, Nanos: 999999999},
+		want:  `"9999-12-31T23:59:59.999999999Z"`,
+	}, {
+		desc:  "Timestamp min value",
+		input: &knownpb.Timestamp{Seconds: -62135596800},
+		want:  `"0001-01-01T00:00:00Z"`,
 	}, {
 		desc:    "Timestamp with +secs out of range",
 		input:   &knownpb.Timestamp{Seconds: 253402300800},
diff --git a/encoding/jsonpb/well_known_types.go b/encoding/jsonpb/well_known_types.go
index 512adc2e..19c82302 100644
--- a/encoding/jsonpb/well_known_types.go
+++ b/encoding/jsonpb/well_known_types.go
@@ -644,10 +644,10 @@ func (o MarshalOptions) marshalDuration(m pref.Message) error {
 	secs := secsVal.Int()
 	nanos := nanosVal.Int()
 	if secs < -maxSecondsInDuration || secs > maxSecondsInDuration {
-		return errors.New("%s: seconds out of range", msgType.FullName())
+		return errors.New("%s: seconds out of range %v", msgType.FullName(), secs)
 	}
-	if nanos <= -secondsInNanos || nanos >= secondsInNanos {
-		return errors.New("%s: nanos out of range", msgType.FullName())
+	if nanos < -secondsInNanos || nanos > secondsInNanos {
+		return errors.New("%s: nanos out of range %v", msgType.FullName(), nanos)
 	}
 	if (secs > 0 && nanos < 0) || (secs < 0 && nanos > 0) {
 		return errors.New("%s: signs of seconds and nanos do not match", msgType.FullName())
@@ -834,10 +834,10 @@ func (o MarshalOptions) marshalTimestamp(m pref.Message) error {
 	secs := secsVal.Int()
 	nanos := nanosVal.Int()
 	if secs < minTimestampSeconds || secs > maxTimestampSeconds {
-		return errors.New("%s: seconds out of range %q", msgType.FullName(), secs)
+		return errors.New("%s: seconds out of range %v", msgType.FullName(), secs)
 	}
-	if nanos < 0 || nanos >= secondsInNanos {
-		return errors.New("%s: nanos out of range %q", msgType.FullName(), nanos)
+	if nanos < 0 || nanos > secondsInNanos {
+		return errors.New("%s: nanos out of range %v", msgType.FullName(), nanos)
 	}
 	// Uses RFC 3339, where generated output will be Z-normalized and uses 0, 3,
 	// 6 or 9 fractional digits.