diff --git a/elasticsearch/query.go b/elasticsearch/query.go
index 285d426..1167012 100644
--- a/elasticsearch/query.go
+++ b/elasticsearch/query.go
@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io"
 	"log"
diff --git a/errors.go b/errors.go
new file mode 100644
index 0000000..553ce65
--- /dev/null
+++ b/errors.go
@@ -0,0 +1,5 @@
+package eventstore
+
+import "errors"
+
+var ErrDupEvent = errors.New("duplicate: event already exists")
diff --git a/interface.go b/interface.go
index 6e0f401..53834b5 100644
--- a/interface.go
+++ b/interface.go
@@ -15,9 +15,9 @@ type Storage interface {
 	// QueryEvents is invoked upon a client's REQ as described in NIP-01.
 	// it should return a channel with the events as they're recovered from a database.
 	// the channel should be closed after the events are all delivered.
-	QueryEvents(ctx context.Context, filter *nostr.Filter) (chan *nostr.Event, error)
+	QueryEvents(context.Context, nostr.Filter) (chan *nostr.Event, error)
 	// DeleteEvent is used to handle deletion events, as per NIP-09.
-	DeleteEvent(ctx context.Context, id string, pubkey string) error
+	DeleteEvent(context.Context, *nostr.Event) error
 	// SaveEvent is called once Relay.AcceptEvent reports true.
-	SaveEvent(ctx context.Context, event *nostr.Event) error
+	SaveEvent(context.Context, *nostr.Event) error
 }
diff --git a/postgresql/save.go b/postgresql/save.go
index 6552649..7120fa0 100644
--- a/postgresql/save.go
+++ b/postgresql/save.go
@@ -4,7 +4,7 @@ import (
 	"context"
 	"encoding/json"
 
-	"github.com/fiatjaf/khatru"
+	"github.com/fiatjaf/eventstore"
 	"github.com/nbd-wtf/go-nostr"
 )
 
@@ -21,7 +21,7 @@ func (b *PostgresBackend) SaveEvent(ctx context.Context, evt *nostr.Event) error
 	}
 
 	if nr == 0 {
-		return khatru.ErrDupEvent
+		return eventstore.ErrDupEvent
 	}
 
 	return nil
diff --git a/sqlite3/save.go b/sqlite3/save.go
index 5268994..f386c3e 100644
--- a/sqlite3/save.go
+++ b/sqlite3/save.go
@@ -4,7 +4,7 @@ import (
 	"context"
 	"encoding/json"
 
-	"github.com/fiatjaf/khatru"
+	"github.com/fiatjaf/eventstore"
 	"github.com/nbd-wtf/go-nostr"
 )
 
@@ -25,7 +25,7 @@ func (b *SQLite3Backend) SaveEvent(ctx context.Context, evt *nostr.Event) error
 	}
 
 	if nr == 0 {
-		return storage.ErrDupEvent
+		return eventstore.ErrDupEvent
 	}
 
 	return nil