diff --git a/filter.go b/filter.go
index e6c0eb6..5cf8630 100644
--- a/filter.go
+++ b/filter.go
@@ -13,22 +13,27 @@ func (fn MatcherFunc) Match(event Event) bool {
 	return fn(event)
 }
 
-// Filter provides an event sink that sends only events that are accepted by a
-// Matcher. No methods on filter are goroutine safe.
-type Filter struct {
+// Filter is the concrete implementation returned by [NewFilter].
+//
+// Deprecated: Filter should not be constructed directly. Use [NewFilter] instead.
+type Filter = filter
+
+type filter struct {
 	dst     Sink
 	matcher Matcher
 	closed  bool
 }
 
-// NewFilter returns a new filter that will send to events to dst that return
-// true for Matcher.
+// NewFilter returns a new event sink that forwards only events accepted by
+// matcher to dst.
+//
+// The returned Sink's methods are not safe for concurrent use.
 func NewFilter(dst Sink, matcher Matcher) Sink {
-	return &Filter{dst: dst, matcher: matcher}
+	return &filter{dst: dst, matcher: matcher}
 }
 
 // Write an event to the filter.
-func (f *Filter) Write(event Event) error {
+func (f *filter) Write(event Event) error {
 	if f.closed {
 		return ErrSinkClosed
 	}
@@ -41,7 +46,7 @@ func (f *Filter) Write(event Event) error {
 }
 
 // Close the filter and allow no more events to pass through.
-func (f *Filter) Close() error {
+func (f *filter) Close() error {
 	// TODO(stevvooe): Not all sinks should have Close.
 	if f.closed {
 		return nil
diff --git a/filter_test.go b/filter_test.go
index 18ccd8a..e61d908 100644
--- a/filter_test.go
+++ b/filter_test.go
@@ -5,16 +5,16 @@ import "testing"
 func TestFilter(t *testing.T) {
 	const nevents = 100
 	ts := newTestSink(t, nevents/2)
-	filter := NewFilter(ts, MatcherFunc(func(event Event) bool {
+	f := NewFilter(ts, MatcherFunc(func(event Event) bool {
 		i, ok := event.(int)
 		return ok && i%2 == 0
 	}))
 
 	for i := range nevents {
-		if err := filter.Write(i); err != nil {
+		if err := f.Write(i); err != nil {
 			t.Fatalf("unexpected error writing event: %v", err)
 		}
 	}
 
-	checkClose(t, filter)
+	checkClose(t, f)
 }