diff --git a/crates/adapters/activitypub/src/instance_actor.rs b/crates/adapters/activitypub/src/instance_actor.rs
new file mode 100644
index 0000000..77192f0
--- /dev/null
+++ b/crates/adapters/activitypub/src/instance_actor.rs
@@ -0,0 +1,57 @@
+use std::sync::Arc;
+
+use async_trait::async_trait;
+use k_ap::{ApActorType, ApUser, ApUserRepository};
+
+pub const INSTANCE_ACTOR_ID: uuid::Uuid =
+    uuid::Uuid::from_bytes([0, 0, 0, 0, 0, 0, 0x40, 0, 0x80, 0, 0, 0, 0, 0, 0, 0]);
+
+pub struct InstanceActorUserRepo {
+    inner: Arc<dyn ApUserRepository>,
+    base_url: String,
+}
+
+impl InstanceActorUserRepo {
+    pub fn new(inner: Arc<dyn ApUserRepository>, base_url: String) -> Self {
+        Self { inner, base_url }
+    }
+}
+
+fn instance_ap_user(base_url: &str) -> ApUser {
+    ApUser {
+        id: INSTANCE_ACTOR_ID,
+        username: "instance".to_string(),
+        display_name: None,
+        bio: None,
+        avatar_url: None,
+        banner_url: None,
+        also_known_as: vec![],
+        profile_url: url::Url::parse(base_url).ok(),
+        attachment: vec![],
+        manually_approves_followers: false,
+        discoverable: false,
+        actor_type: ApActorType::Service,
+        featured_url: None,
+    }
+}
+
+#[async_trait]
+impl ApUserRepository for InstanceActorUserRepo {
+    async fn find_by_id(&self, id: uuid::Uuid) -> anyhow::Result<Option<ApUser>> {
+        if id == INSTANCE_ACTOR_ID {
+            return Ok(Some(instance_ap_user(&self.base_url)));
+        }
+        self.inner.find_by_id(id).await
+    }
+
+    async fn find_by_username(&self, username: &str) -> anyhow::Result<Option<ApUser>> {
+        if username == "instance" {
+            return Ok(Some(instance_ap_user(&self.base_url)));
+        }
+        self.inner.find_by_username(username).await
+    }
+
+    async fn count_users(&self) -> anyhow::Result<usize> {
+        self.inner.count_users().await
+    }
+}
diff --git a/crates/adapters/activitypub/src/lib.rs b/crates/adapters/activitypub/src/lib.rs
index 749aa65..af65e9e 100644
--- a/crates/adapters/activitypub/src/lib.rs
+++ b/crates/adapters/activitypub/src/lib.rs
@@ -1,6 +1,7 @@
 pub mod composite_handler;
 pub mod event_handler;
 pub mod federation_event_bridge;
+pub mod instance_actor;
 pub mod objects;
 pub mod port;
 pub mod remote_review_repository;
@@ -96,16 +97,18 @@ pub async fn wire(deps: ActivityPubDeps) -> anyhow::Result<ActivityPubWire> {
         federation_event_bridge::FederationEventBridge::new(event_publisher),
     );
 
+    let user_repo = std::sync::Arc::new(instance_actor::InstanceActorUserRepo::new(
+        std::sync::Arc::new(DomainUserRepoAdapter::new(user_repo, base_url.clone())),
+        base_url.clone(),
+    ));
     let concrete = std::sync::Arc::new(
         ActivityPubService::builder(base_url.clone())
             .activity_repo(activity_repo)
             .follow_repo(follow_repo)
             .actor_repo(actor_repo)
             .blocklist_repo(blocklist_repo)
-            .user_repo(std::sync::Arc::new(DomainUserRepoAdapter::new(
-                user_repo,
-                base_url.clone(),
-            )))
+            .user_repo(user_repo)
+            .signed_fetch_actor_id(instance_actor::INSTANCE_ACTOR_ID)
             .content_reader(composite.clone() as std::sync::Arc<dyn ApContentReader>)
             .object_handler(composite as std::sync::Arc<dyn ApObjectHandler>)
             .event_publisher(fed_event_bridge)