diff --git a/src/activitypub/authentication.rs b/src/activitypub/authentication.rs
index 96ebc3d..f55ab41 100644
--- a/src/activitypub/authentication.rs
+++ b/src/activitypub/authentication.rs
@@ -32,6 +32,9 @@ pub enum AuthenticationError {
     #[error(transparent)]
     HttpSignatureError(#[from] HttpSignatureError),
 
+    #[error("no HTTP signature")]
+    NoHttpSignature,
+
     #[error(transparent)]
     JsonSignatureError(#[from] JsonSignatureError),
 
@@ -76,11 +79,17 @@ pub async fn verify_signed_request(
     request: &HttpRequest,
     no_fetch: bool,
 ) -> Result<DbActorProfile, AuthenticationError> {
-    let signature_data = parse_http_signature(
+    let signature_data = match parse_http_signature(
         request.method(),
         request.uri(),
         request.headers(),
-    )?;
+    ) {
+        Ok(signature_data) => signature_data,
+        Err(HttpSignatureError::NoSignature) => {
+            return Err(AuthenticationError::NoHttpSignature);
+        },
+        Err(other_error) => return Err(other_error.into()),
+    };
 
     let actor_id = key_id_to_actor_id(&signature_data.key_id)?;
     let actor_profile = if no_fetch {
@@ -113,12 +122,13 @@ pub async fn verify_signed_activity(
     db_client: &impl GenericClient,
     activity: &Value,
 ) -> Result<DbActorProfile, AuthenticationError> {
-    let signature_data = get_json_signature(activity).map_err(|error| {
-        match error {
-            JsonSignatureError::NoProof => AuthenticationError::NoJsonSignature,
-            other_error => other_error.into(),
-        }
-    })?;
+    let signature_data = match get_json_signature(activity) {
+        Ok(signature_data) => signature_data,
+        Err(JsonSignatureError::NoProof) => {
+            return Err(AuthenticationError::NoJsonSignature);
+        },
+        Err(other_error) => return Err(other_error.into()),
+    };
 
     let actor_profile = match signature_data.signer {
         JsonSigner::ActorKeyId(ref key_id) => {
diff --git a/src/activitypub/receiver.rs b/src/activitypub/receiver.rs
index 6ea4432..0fa9bc8 100644
--- a/src/activitypub/receiver.rs
+++ b/src/activitypub/receiver.rs
@@ -157,6 +157,8 @@ pub async fn receive_activity(
         let object_id = find_object_id(&activity.object)?;
         activity.actor == object_id
     } else { false };
+
+    // HTTP signature is required
     let mut signer = match verify_signed_request(
         config,
         db_client,
@@ -169,8 +171,13 @@ pub async fn receive_activity(
             request_signer
         },
         Err(error) => {
-            if is_self_delete {
+            if is_self_delete && matches!(
+                error,
+                AuthenticationError::NoHttpSignature |
+                AuthenticationError::DatabaseError(_)
+            ) {
                 // Ignore Delete(Person) activities without HTTP signatures
+                // or if signer is not found in local database
                 return Ok(());
             };
             log::warn!("invalid HTTP signature: {}", error);
@@ -178,7 +185,7 @@ pub async fn receive_activity(
         },
     };
 
-    // Verify embedded signature
+    // JSON signature is optional
     match verify_signed_activity(config, db_client, activity_raw).await {
         Ok(activity_signer) => {
             if activity_signer.acct != signer.acct {
diff --git a/src/http_signatures/verify.rs b/src/http_signatures/verify.rs
index 15e29e9..0a955cd 100644
--- a/src/http_signatures/verify.rs
+++ b/src/http_signatures/verify.rs
@@ -13,6 +13,9 @@ const SIGNATURE_EXPIRES_IN: i64 = 12; // 12 hours
 
 #[derive(thiserror::Error, Debug)]
 pub enum HttpSignatureVerificationError {
+    #[error("missing signature header")]
+    NoSignature,
+
     #[error("{0}")]
     HeaderError(&'static str),
 
@@ -41,7 +44,7 @@ pub fn parse_http_signature(
     request_headers: &HeaderMap,
 ) -> Result<HttpSignatureData, VerificationError> {
     let signature_header = request_headers.get("signature")
-        .ok_or(VerificationError::HeaderError("missing signature header"))?
+        .ok_or(VerificationError::NoSignature)?
         .to_str()
         .map_err(|_| VerificationError::HeaderError("invalid signature header"))?;