diff --git a/mcp/content.go b/mcp/content.go
index fb1a0d1e..8a832d7d 100644
--- a/mcp/content.go
+++ b/mcp/content.go
@@ -88,7 +88,7 @@ type AudioContent struct {
 	Annotations *Annotations
 }
 
-func (c AudioContent) MarshalJSON() ([]byte, error) {
+func (c *AudioContent) MarshalJSON() ([]byte, error) {
 	// Custom wire format to ensure required fields are always included, even when empty.
 	data := c.Data
 	if data == nil {