diff --git a/client/transport/sse.go b/client/transport/sse.go
index 3cc7e98ee..b85fb6caf 100644
--- a/client/transport/sse.go
+++ b/client/transport/sse.go
@@ -363,6 +363,12 @@ func (c *SSE) SendRequest(
 		req.Header.Set(k, v)
 	}
 
+	for k, v := range request.Header {
+		if _, ok := req.Header[k]; !ok {
+			req.Header[k] = v
+		}
+	}
+
 	// Add OAuth authorization if configured
 	if c.oauthHandler != nil {
 		authHeader, err := c.oauthHandler.GetAuthorizationHeader(ctx)