diff --git a/core/core.go b/core/core.go
index ddb6e9ba61..9d2877a165 100644
--- a/core/core.go
+++ b/core/core.go
@@ -7,6 +7,7 @@ import (
 	"math/big"
 	"sort"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/dominant-strategies/go-quai/common"