diff --git a/internal/chunks/chunk.go b/internal/chunks/chunk.go
index f2b55c3..f8e8e1d 100644
--- a/internal/chunks/chunk.go
+++ b/internal/chunks/chunk.go
@@ -8,10 +8,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io"
-	"os"
 	"slices"
-
-	"fyne.io/fyne/v2"
 )
 
 // IFFChunk represents a chunk in an IFF file.
@@ -34,24 +31,11 @@ type IFFChunk struct {
 }
 
 // ReadIFFFile reads an IFF file and returns the root chunk.
+// fileLen is the length of the file in bytes.
 // In case of an error, the function returns nil and the error.
-func ReadIFFFile(reader fyne.URIReadCloser) (*IFFChunk, error) {
-	// TODO: get rid of fyne.URIReadCloser
-	var chunk *IFFChunk
-
-	file, err := os.Open(reader.URI().Path())
-	if err != nil {
-		return nil, err
-	}
-	defer file.Close()
-
-	fileInfo, err := file.Stat()
-	if err != nil {
-		return nil, err
-	}
-	fileLen := fileInfo.Size()
+func ReadIFFFile(reader io.Reader, fileLen int64) (*IFFChunk, error) {
 
-	chunk, err = readChunk(reader, nil, fileLen, 0)
+	chunk, err := readChunk(reader, nil, fileLen, 0)
 
 	return chunk, err
 }
diff --git a/internal/gui/gui.go b/internal/gui/gui.go
index 67851d4..38f5176 100644
--- a/internal/gui/gui.go
+++ b/internal/gui/gui.go
@@ -5,6 +5,9 @@
 package gui
 
 import (
+	"bytes"
+	"io"
+
 	"fyne.io/fyne/v2"
 	"fyne.io/fyne/v2/app"
 	"fyne.io/fyne/v2/container"
@@ -58,7 +61,15 @@ func OpenGUI(version string) {
 
 				appData.topContainer.Refresh()
 
-				appData.chunks, err = chunks.ReadIFFFile(reader)
+				// read the file to get its length
+				data, err := io.ReadAll(reader)
+				if err != nil {
+					dialog.ShowError(err, appData.win)
+					return
+				}
+
+				appData.chunks, err = chunks.ReadIFFFile(bytes.NewReader(data),
+					int64(len(data)))
 				if err != nil {
 					dialog.ShowError(err, appData.win)
 					return