diff --git a/lib/model/folder.go b/lib/model/folder.go
index 9f50fc80c..fb6051546 100644
--- a/lib/model/folder.go
+++ b/lib/model/folder.go
@@ -745,12 +745,19 @@ func (f *folder) scanSubdirsChangedAndNew(ctx context.Context, subDirs []string,
 		switch f.Type {
 		case config.FolderTypeReceiveOnly, config.FolderTypeReceiveEncrypted:
 		default:
-			if nf, ok := f.findRename(ctx, res.File, batch); ok {
-				if ok, err := batch.Update(nf); err != nil {
-					return 0, err
-				} else if ok {
-					changes++
-					batch.markDeleted(nf.Name)
+			// Rename detection is comparatively expensive, so only attempt
+			// it for files that appeared as new on disk during this scan. A
+			// rename that overwrites an existing file (the destination path
+			// already had an entry, so it scans as an update rather than a
+			// new file) is not optimised as a rename.
+			if res.File.New && res.File.Size > 0 {
+				if nf, ok := f.findRename(ctx, res.File, batch); ok {
+					if ok, err := batch.Update(nf); err != nil {
+						return 0, err
+					} else if ok {
+						changes++
+						batch.markDeleted(nf.Name)
+					}
 				}
 			}
 		}
diff --git a/lib/model/model_test.go b/lib/model/model_test.go
index 1964c05ff..8cac582eb 100644
--- a/lib/model/model_test.go
+++ b/lib/model/model_test.go
@@ -3270,17 +3270,20 @@ func TestRenameSequenceOrder(t *testing.T) {
 		t.Errorf("Unexpected count: %d != %d", count, numFiles)
 	}
 
-	// Modify all the files, other than the ones we expect to rename
+	// Modify all the files other than the rename sources, whose content we
+	// keep intact so the renamed copies still match by block hash.
 	for i := 0; i < numFiles; i++ {
-		if i == 3 || i == 17 || i == 16 || i == 4 {
+		if i == 3 || i == 16 {
 			continue
 		}
 		v := fmt.Sprintf("%d", i)
 		writeFile(t, ffs, v, []byte(v+"-new"))
 	}
-	// Rename
-	must(t, ffs.Rename("3", "17"))
-	must(t, ffs.Rename("16", "4"))
+	// Rename to previously unseen names. Renaming onto an existing name is
+	// treated as an in-place update rather than a rename, since rename
+	// detection only runs for files that are new on disk.
+	must(t, ffs.Rename("3", "20"))
+	must(t, ffs.Rename("16", "21"))
 
 	// Scan
 	m.ScanFolders()
@@ -3291,10 +3294,10 @@ func TestRenameSequenceOrder(t *testing.T) {
 	it, errFn := m.LocalFilesSequenced("default", protocol.LocalDeviceID, 0)
 	for i := range it {
 		t.Log(i)
-		if i.FileName() == "17" {
+		if i.FileName() == "20" {
 			firstExpectedSequence = i.SequenceNo() + 1
 		}
-		if i.FileName() == "4" {
+		if i.FileName() == "21" {
 			secondExpectedSequence = i.SequenceNo() + 1
 		}
 		if i.FileName() == "3" {
diff --git a/lib/protocol/bep_fileinfo.go b/lib/protocol/bep_fileinfo.go
index 329ce5a58..ad3d17e6c 100644
--- a/lib/protocol/bep_fileinfo.go
+++ b/lib/protocol/bep_fileinfo.go
@@ -146,6 +146,8 @@ type FileInfo struct {
 	Deleted       bool
 	NoPermissions bool
 
+	New bool // set by the scanner when the file newly appeared on disk; no db / wire representation
+
 	truncated bool // was created from a truncated file info without blocks
 }
 
@@ -233,7 +235,8 @@ func (f *FileInfo) LogAttr() slog.Attr {
 	case FileInfoTypeFile:
 		kind = "file"
 		if !f.Deleted {
-			attrs = append(attrs,
+			attrs = append(
+				attrs,
 				slog.Any("modified", f.ModTime()),
 				slog.String("permissions", fmt.Sprintf("0%03o", f.Permissions)),
 				slog.Int64("size", f.Size),
diff --git a/lib/scanner/walk.go b/lib/scanner/walk.go
index 479beeb08..2b8bfb5d4 100644
--- a/lib/scanner/walk.go
+++ b/lib/scanner/walk.go
@@ -471,6 +471,8 @@ func (w *walker) walkRegular(ctx context.Context, relPath string, info fs.FileIn
 	f.RawBlockSize = int32(blockSize)
 	l.Debugln(w, "checking:", f)
 
+	f.New = !hasCurFile
+
 	if hasCurFile {
 		if curFile.IsEquivalentOptional(f, protocol.FileInfoComparison{
 			ModTimeWindow:   w.ModTimeWindow,
@@ -518,6 +520,8 @@ func (w *walker) walkDir(ctx context.Context, relPath string, info fs.FileInfo,
 	f.NoPermissions = w.IgnorePerms
 	l.Debugln(w, "checking:", f)
 
+	f.New = !hasCurFile
+
 	if hasCurFile {
 		if curFile.IsEquivalentOptional(f, protocol.FileInfoComparison{
 			ModTimeWindow:   w.ModTimeWindow,
@@ -570,6 +574,8 @@ func (w *walker) walkSymlink(ctx context.Context, relPath string, info fs.FileIn
 	f = w.updateFileInfo(f, curFile)
 	l.Debugln(w, "checking:", f)
 
+	f.New = !hasCurFile
+
 	if hasCurFile {
 		if curFile.IsEquivalentOptional(f, protocol.FileInfoComparison{
 			ModTimeWindow:   w.ModTimeWindow,