diff --git a/backend/union/policy/eplus.go b/backend/union/policy/eplus.go
index d1aad2c9e..57f97c231 100644
--- a/backend/union/policy/eplus.go
+++ b/backend/union/policy/eplus.go
@@ -42,7 +42,7 @@ func (p *EpLus) lusEntries(entries []upstream.Entry) (upstream.Entry, error) {
 	var minUsedSpace int64 = math.MaxInt64
 	var lusEntry upstream.Entry
 	for _, e := range entries {
-		space, err := e.UpstreamFs().GetFreeSpace()
+		space, err := e.UpstreamFs().GetUsedSpace()
 		if err != nil {
 			fs.LogPrintf(fs.LogLevelNotice, nil,
 				"Used Space is not supported for upstream %s, treating as 0", e.UpstreamFs().Name())