diff --git a/internal/sevenzip/reader.go b/internal/sevenzip/reader.go
index 651ac7b..ebd05aa 100644
--- a/internal/sevenzip/reader.go
+++ b/internal/sevenzip/reader.go
@@ -19,6 +19,7 @@ import (
 
 	"bookhoard/internal/sevenzip/internal/pool"
 	"bookhoard/internal/sevenzip/internal/util"
+
 	"github.com/bodgit/plumbing"
 	"github.com/spf13/afero"
 )
@@ -415,6 +416,10 @@ func (z *Reader) init(r io.ReaderAt, size int64) (err error) {
 		return err
 	}
 
+	if sr == nil {
+		return errFormat
+	}
+
 	// Work out where we are in the file (32, avoiding magic numbers)
 	if z.start, err = sr.Seek(0, io.SeekCurrent); err != nil {
 		return fmt.Errorf("sevenzip: error seeking current position: %w", err)