diff --git a/modules/timeutil/datetime.go b/modules/timeutil/datetime.go
index 83170b374b54c..6757c11cb6c56 100644
--- a/modules/timeutil/datetime.go
+++ b/modules/timeutil/datetime.go
@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"html"
 	"html/template"
+	"strconv"
 	"time"
 )
 
@@ -58,3 +59,22 @@ func DateTime(format string, datetime any) template.HTML {
 	}
 	panic(fmt.Sprintf("Unsupported format %s", format))
 }
+
+func ParseDateTimeGraceful(datetime any) (time.Time, error) {
+	switch val := datetime.(type) {
+	case string:
+		if timestamp, err := strconv.ParseInt(val, 10, 64); err == nil {
+			return time.Unix(val, 0), nil
+		}
+
+		t, err := time.Parse(time.RFC3339, val)
+		if err != nil {
+			return time.Time{}, err
+		}
+		return t, nil
+	case int64:
+		return time.Unix(val, 0), nil
+	default:
+		return time.Time{}, fmt.Errorf("unsupported data type: %T", datetime)
+	}
+}
diff --git a/modules/timeutil/datetime_test.go b/modules/timeutil/datetime_test.go
index f44b7aaae3c1b..898391eb5691e 100644
--- a/modules/timeutil/datetime_test.go
+++ b/modules/timeutil/datetime_test.go
@@ -43,3 +43,71 @@ func TestDateTime(t *testing.T) {
 	actual = DateTime("full", refTimeStamp)
 	assert.EqualValues(t, `<relative-time format="datetime" weekday="" year="numeric" month="short" day="numeric" hour="numeric" minute="numeric" second="numeric" datetime="2017-12-31T19:00:00-05:00">2017-12-31 19:00:00 -05:00</relative-time>`, actual)
 }
+
+func TestParseDateTimeGraceful(t *testing.T) {
+	testData := []struct {
+		value    any
+		expected any
+		isFail   bool
+	}{
+		{
+			value:    "2006-01-02T15:04:05Z",
+			expected: int64(1136214245),
+		},
+		{
+			value:    "2006-01-02T15:04:05.999Z",
+			expected: int64(1136214245),
+		},
+		{
+			value:    "2006-01-02T15:04:05-07:00",
+			expected: int64(1136239445),
+		},
+		{
+			value:    "2006-01-02T15:04:05.999-07:00",
+			expected: int64(1136239445),
+		},
+		{
+			value:    int64(1136214245),
+			expected: int64(1136214245),
+		},
+		{
+			value:    "1136214245",
+			expected: int64(1136214245),
+		},
+		{
+			value:    int64(1622040867000),
+			expected: int64(1622040867000),
+		},
+		{
+			value:    "1622040867000",
+			expected: int64(1622040867000),
+		},
+		{
+			value:    0,
+			expected: int64(-62135596800),
+			isFail:   true,
+		},
+		{
+			value:    nil,
+			expected: int64(-62135596800),
+			isFail:   true,
+		},
+		{
+			value:    "",
+			expected: int64(-62135596800),
+			isFail:   true,
+		},
+	}
+
+	for _, testCase := range testData {
+		actual, err := ParseDateTimeGraceful(testCase.value)
+
+		if testCase.isFail == true {
+			assert.NotNil(t, err)
+			assert.True(t, actual.IsZero())
+		} else {
+			assert.Nil(t, err)
+			assert.EqualValues(t, testCase.expected, actual.Unix())
+		}
+	}
+}
diff --git a/routers/api/v1/notify/repo.go b/routers/api/v1/notify/repo.go
index bd3b86a6f1525..744fe9bc70274 100644
--- a/routers/api/v1/notify/repo.go
+++ b/routers/api/v1/notify/repo.go
@@ -6,12 +6,12 @@ package notify
 import (
 	"net/http"
 	"strings"
-	"time"
 
 	activities_model "code.gitea.io/gitea/models/activities"
 	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/modules/timeutil"
 	"code.gitea.io/gitea/services/convert"
 )
 
@@ -181,7 +181,7 @@ func ReadRepoNotifications(ctx *context.APIContext) {
 	lastRead := int64(0)
 	qLastRead := ctx.FormTrim("last_read_at")
 	if len(qLastRead) > 0 {
-		tmpLastRead, err := time.Parse(time.RFC3339, qLastRead)
+		tmpLastRead, err := timeutil.ParseDateTimeGraceful(qLastRead)
 		if err != nil {
 			ctx.InternalServerError(err)
 			return
diff --git a/routers/api/v1/notify/user.go b/routers/api/v1/notify/user.go
index 2261610c09238..02c1de512c037 100644
--- a/routers/api/v1/notify/user.go
+++ b/routers/api/v1/notify/user.go
@@ -5,11 +5,11 @@ package notify
 
 import (
 	"net/http"
-	"time"
 
 	activities_model "code.gitea.io/gitea/models/activities"
 	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/modules/timeutil"
 	"code.gitea.io/gitea/services/convert"
 )
 
@@ -130,11 +130,12 @@ func ReadNotifications(ctx *context.APIContext) {
 	lastRead := int64(0)
 	qLastRead := ctx.FormTrim("last_read_at")
 	if len(qLastRead) > 0 {
-		tmpLastRead, err := time.Parse(time.RFC3339, qLastRead)
+		tmpLastRead, err := timeutil.ParseDateTimeGraceful(qLastRead)
 		if err != nil {
 			ctx.InternalServerError(err)
 			return
 		}
+
 		if !tmpLastRead.IsZero() {
 			lastRead = tmpLastRead.Unix()
 		}
diff --git a/tests/integration/api_notification_test.go b/tests/integration/api_notification_test.go
index 0ff13704cf69d..79bbc042ffb69 100644
--- a/tests/integration/api_notification_test.go
+++ b/tests/integration/api_notification_test.go
@@ -115,8 +115,12 @@ func TestAPINotification(t *testing.T) {
 	DecodeJSON(t, resp, &apiNL)
 	assert.Len(t, apiNL, 2)
 
-	lastReadAt := "2000-01-01T00%3A50%3A01%2B00%3A00" // 946687801 <- only Notification 4 is in this filter ...
-	req = NewRequest(t, "PUT", fmt.Sprintf("/api/v1/repos/%s/%s/notifications?last_read_at=%s&token=%s", user2.Name, repo1.Name, lastReadAt, token))
+	lastReadAt1 := "2000-01-01T00%3A50%3A01%2B00%3A00" // 946687801 <- only Notification 4 is in this filter ...
+	req = NewRequest(t, "PUT", fmt.Sprintf("/api/v1/repos/%s/%s/notifications?last_read_at=%s&token=%s", user2.Name, repo1.Name, lastReadAt1, token))
+	MakeRequest(t, req, http.StatusResetContent)
+
+	lastReadAt2 := "946687801"
+	req = NewRequest(t, "PUT", fmt.Sprintf("/api/v1/repos/%s/%s/notifications?last_read_at=%s&token=%s", user2.Name, repo1.Name, lastReadAt2, token))
 	MakeRequest(t, req, http.StatusResetContent)
 
 	req = NewRequest(t, "GET", fmt.Sprintf("/api/v1/notifications?status-types=unread&token=%s", token))