diff --git a/weed/shell/command_ec_common.go b/weed/shell/command_ec_common.go
index 3616c4e16..f059b4e74 100644
--- a/weed/shell/command_ec_common.go
+++ b/weed/shell/command_ec_common.go
@@ -678,11 +678,16 @@ func countShardsByRack(vid needle.VolumeId, locations []*EcNode) map[string]int
 func (ecb *ecBalancer) doBalanceEcShardsAcrossRacks(collection string, vid needle.VolumeId, locations []*EcNode) error {
 	racks := ecb.racks()
 
-	// calculate average number of shards an ec rack should have for one volume
-	averageShardsPerEcRack := ceilDivide(erasure_coding.TotalShardsCount, len(racks))
-
 	// see the volume's shards are in how many racks, and how many in each rack
 	rackToShardCount := countShardsByRack(vid, locations)
+
+	// Calculate actual total shards for this volume (not hardcoded default)
+	var totalShardsForVolume int
+	for _, count := range rackToShardCount {
+		totalShardsForVolume += count
+	}
+	// calculate average number of shards an ec rack should have for one volume
+	averageShardsPerEcRack := ceilDivide(totalShardsForVolume, len(racks))
 	rackEcNodesWithVid := groupBy(locations, func(ecNode *EcNode) string {
 		return string(ecNode.rack)
 	})
diff --git a/weed/topology/topology_ec.go b/weed/topology/topology_ec.go
index 7097cb84b..88fcf5c8d 100644
--- a/weed/topology/topology_ec.go
+++ b/weed/topology/topology_ec.go
@@ -91,6 +91,10 @@ func NewEcShardLocations(collection string) *EcShardLocations {
 }
 
 func (loc *EcShardLocations) AddShard(shardId erasure_coding.ShardId, dn *DataNode) (added bool) {
+	// Defensive bounds check to prevent panic with out-of-range shard IDs
+	if int(shardId) >= erasure_coding.MaxShardCount {
+		return false
+	}
 	dataNodes := loc.Locations[shardId]
 	for _, n := range dataNodes {
 		if n.Id() == dn.Id() {
@@ -102,6 +106,10 @@ func (loc *EcShardLocations) AddShard(shardId erasure_coding.ShardId, dn *DataNo
 }
 
 func (loc *EcShardLocations) DeleteShard(shardId erasure_coding.ShardId, dn *DataNode) (deleted bool) {
+	// Defensive bounds check to prevent panic with out-of-range shard IDs
+	if int(shardId) >= erasure_coding.MaxShardCount {
+		return false
+	}
 	dataNodes := loc.Locations[shardId]
 	foundIndex := -1
 	for index, n := range dataNodes {