diff --git a/weed/format/layout.go b/weed/format/layout.go
index 1ba4aeb10b..c472635258 100644
--- a/weed/format/layout.go
+++ b/weed/format/layout.go
@@ -16,6 +16,8 @@ const (
 	MaxExtentCount = 1 << 20
 	// MaxPayloadBytes bounds the adapter payload carried in entry metadata.
 	MaxPayloadBytes = 16 << 20
+	// MaxFormatNameBytes bounds the encoded adapter name.
+	MaxFormatNameBytes = 256
 )
 
 // TotalSize returns the file size the layout describes.
@@ -44,6 +46,9 @@ func (l *Layout) Validate(fileSize int64) error {
 	if l.Format == "" {
 		return fmt.Errorf("layout has no format name")
 	}
+	if len(l.Format) > MaxFormatNameBytes {
+		return fmt.Errorf("layout format name is too long: %d bytes", len(l.Format))
+	}
 	if l.Align < 1 {
 		return fmt.Errorf("layout align %d is invalid", l.Align)
 	}
@@ -97,7 +102,7 @@ func DecodeLayout(data []byte) (*Layout, error) {
 	if err != nil || version != layoutVersion {
 		return nil, fmt.Errorf("unsupported layout version")
 	}
-	name, err := readUvarintBytes(reader, 256)
+	name, err := readUvarintBytes(reader, MaxFormatNameBytes)
 	if err != nil {
 		return nil, fmt.Errorf("read layout format: %w", err)
 	}
diff --git a/weed/format/layout_test.go b/weed/format/layout_test.go
index 81b25e3a7c..5139b848fe 100644
--- a/weed/format/layout_test.go
+++ b/weed/format/layout_test.go
@@ -66,6 +66,7 @@ func TestLayoutValidate(t *testing.T) {
 		{"no extents", Layout{Format: "x", Align: 1}, -1, "no extents"},
 		{"bad align", Layout{Format: "x", ExtentSizes: []int64{5}, Align: 0}, -1, "align"},
 		{"no name", Layout{ExtentSizes: []int64{5}, Align: 1}, -1, "format name"},
+		{"name too long", Layout{Format: strings.Repeat("x", MaxFormatNameBytes+1), ExtentSizes: []int64{5}, Align: 1}, -1, "too long"},
 	}
 	for _, test := range tests {
 		err := test.layout.Validate(test.fileSize)