diff --git a/models/forgefed/activity.go b/models/forgefed/activity.go
index 0820bf5ea6..491a938bd5 100644
--- a/models/forgefed/activity.go
+++ b/models/forgefed/activity.go
@@ -26,9 +26,13 @@ func (s *ForgeLike) UnmarshalJSON(data []byte) error {
 func (s ForgeLike) Validate() []string {
 	var result []string
 	result = append(result, validation.ValidateNotEmpty(string(s.Type), "type")...)
+	result = append(result, validation.ValidateOneOf(string(s.Type), []any{"Like"})...)
 	result = append(result, validation.ValidateNotEmpty(s.Actor.GetID().String(), "actor")...)
 	result = append(result, validation.ValidateNotEmpty(s.Object.GetID().String(), "object")...)
 	result = append(result, validation.ValidateNotEmpty(s.StartTime.String(), "startTime")...)
+	if s.StartTime.IsZero() {
+		result = append(result, "StartTime was invalid.")
+	}
 
 	return result
 }
diff --git a/models/forgefed/activity_test.go b/models/forgefed/activity_test.go
index cc82c1b8b4..982ed82eec 100644
--- a/models/forgefed/activity_test.go
+++ b/models/forgefed/activity_test.go
@@ -7,6 +7,7 @@ import (
 	"reflect"
 	"testing"
 
+	"code.gitea.io/gitea/modules/validation"
 	ap "github.com/go-ap/activitypub"
 )
 
@@ -82,3 +83,37 @@ func Test_StarUnmarshalJSON(t *testing.T) {
 		})
 	}
 }
+
+func TestAcivityValidation(t *testing.T) {
+	sut := new(ForgeLike)
+	sut.UnmarshalJSON([]byte(`{"type":"Like",
+	"actor":"https://repo.prod.meissa.de/api/activitypub/user-id/1",
+	"object":"https://codeberg.org/api/activitypub/repository-id/1",
+	"startTime": "2014-12-31T23:00:00-08:00"}`))
+	if res, _ := validation.IsValid(sut); !res {
+		t.Errorf("sut expected to be valid: %v\n", sut.Validate())
+	}
+
+	sut.UnmarshalJSON([]byte(`{"actor":"https://repo.prod.meissa.de/api/activitypub/user-id/1",
+	"object":"https://codeberg.org/api/activitypub/repository-id/1",
+	"startTime": "2014-12-31T23:00:00-08:00"}`))
+	if sut.Validate()[0] != "Field type may not be empty" {
+		t.Errorf("validation error expected but was: %v\n", sut.Validate())
+	}
+
+	sut.UnmarshalJSON([]byte(`{"type":"bad-type",
+		"actor":"https://repo.prod.meissa.de/api/activitypub/user-id/1",
+	"object":"https://codeberg.org/api/activitypub/repository-id/1",
+	"startTime": "2014-12-31T23:00:00-08:00"}`))
+	if sut.Validate()[0] != "Value bad-type is not contained in allowed values [[Like]]" {
+		t.Errorf("validation error expected but was: %v\n", sut.Validate())
+	}
+
+	sut.UnmarshalJSON([]byte(`{"type":"Like",
+		"actor":"https://repo.prod.meissa.de/api/activitypub/user-id/1",
+	"object":"https://codeberg.org/api/activitypub/repository-id/1",
+	"startTime": "not a date"}`))
+	if sut.Validate()[0] != "StartTime was invalid." {
+		t.Errorf("validation error expected but was: %v\n", sut.Validate())
+	}
+}
diff --git a/routers/api/v1/activitypub/repository.go b/routers/api/v1/activitypub/repository.go
index 1d94560127..765ab01fcc 100644
--- a/routers/api/v1/activitypub/repository.go
+++ b/routers/api/v1/activitypub/repository.go
@@ -21,6 +21,7 @@ import (
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/util"
+	"code.gitea.io/gitea/modules/validation"
 	"code.gitea.io/gitea/modules/web"
 	"github.com/google/uuid"
 
@@ -85,7 +86,11 @@ func RepositoryInbox(ctx *context.APIContext) {
 	log.Info("RepositoryInbox: repo: %v", repository)
 
 	activity := web.GetForm(ctx).(*forgefed.ForgeLike)
-	log.Info("RepositoryInbox: activity:%v", activity)
+	if res, err := validation.IsValid(activity); !res {
+		ctx.ServerError("Validate activity", err)
+		return
+	}
+	log.Info("RepositoryInbox: activity validated:%v", activity)
 
 	// parse actorID (person)
 	actorUri := activity.Actor.GetID().String()