diff --git a/grain-pool.go b/grain-pool.go
index 58ed856..f69a8fa 100644
--- a/grain-pool.go
+++ b/grain-pool.go
@@ -129,8 +129,9 @@ func (p *GrainLocalPool) GetGrain(id CartId) (*CartGrain, error) {
 			}
 		}
 		grain, err = p.spawn(id)
-
+		p.mu.Lock()
 		p.grains[id] = grain
+		p.mu.Unlock()
 	}
 	go func() {
 		l := float64(len(p.grains))