diff --git a/models/activitypub/actor.go b/models/activitypub/actor.go
index 9a950cb362..2c877a6ef5 100644
--- a/models/activitypub/actor.go
+++ b/models/activitypub/actor.go
@@ -7,6 +7,7 @@ import (
 	"strings"
 
 	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/validation"
 )
 
 type Validatable interface { // ToDo: What is the right package for this interface?
@@ -40,8 +41,8 @@ func (a ActorID) Validate() []string {
 
 	var err = []string{}
 
-	if res := validate_is_not_empty(a.schema); res != nil {
-		err = append(err, strings.Join([]string{res.Error(), "for schema field"}, " "))
+	if res := validation.ValidateNotEmpty(a.schema, "schema"); res != nil {
+		err = append(err, res.Error())
 	}
 
 	if res := validate_is_not_empty(a.host); res != nil {
@@ -167,3 +168,10 @@ func ParseActorID(validatedURL url.URL, source string) ActorID { // ToDo: Turn t
 		port:   validatedURL.Port(),
 	}
 }
+
+func NewActorId(uri string, source string) (ActorID, error) {
+	if !validation.IsValidExternalURL(uri) {
+		return ActorID{}, fmt.Errorf("uri %s is not a valid external url.", uri)
+	}
+	return ActorID{}, nil
+}
diff --git a/models/activitypub/actor_test.go b/models/activitypub/actor_test.go
index 458d56599a..e8eb6e2d81 100644
--- a/models/activitypub/actor_test.go
+++ b/models/activitypub/actor_test.go
@@ -117,3 +117,20 @@ func TestGetHostAndPort(t *testing.T) {
 	}
 
 }
+
+func TestShouldThrowErrorOnInvalidInput(t *testing.T) {
+	_, err := NewActorId("", "forgejo")
+	if err == nil {
+		t.Errorf("empty input should be invalid.")
+	}
+
+	_, err = NewActorId("http://localhost:3000/api/v1/something", "forgejo")
+	if err == nil {
+		t.Errorf("localhost uris are not external")
+	}
+
+	_, err = NewActorId("https://an.other.host/api/v1/activitypub/person-id/1", "forgejo")
+	if err != nil {
+		t.Errorf("this uri should be valid")
+	}
+}