diff --git a/web/middleware.go b/web/middleware.go
index a8477c5..03e04e7 100644
--- a/web/middleware.go
+++ b/web/middleware.go
@@ -130,6 +130,7 @@ func (m *mStack) alloc() *cStack {
 }
 
 func (m *mStack) release(cs *cStack) {
+	cs.C = C{}
 	if cs.pool != m.pool {
 		return
 	}