diff --git a/consensus/istanbul/core/handler.go b/consensus/istanbul/core/handler.go
index a591fb217a..90d2a215da 100644
--- a/consensus/istanbul/core/handler.go
+++ b/consensus/istanbul/core/handler.go
@@ -36,7 +36,9 @@ func (c *core) Start() error {
 		return err
 	}
 
+	c.currentMu.Lock()
 	c.current = roundState
+	c.currentMu.Unlock()
 	c.roundChangeSetV2 = newRoundChangeSetV2(c.current.ValidatorSet())
 
 	// Reset the Round Change timer for the current round to timeout.