diff --git a/internal/api/multicast.go b/internal/api/multicast.go
index b75276b6..2663484b 100644
--- a/internal/api/multicast.go
+++ b/internal/api/multicast.go
@@ -34,7 +34,7 @@ func (m *Multicast) Num() int {
 // Add adds w to m. Future writes to m will also reach w.
 // If w is already part of m, Add does nothing.
 func (m *Multicast) Add(w io.Writer) {
-	if m == nil {
+	if w == nil {
 		return
 	}