diff --git a/Device/DiskImage.cpp b/Device/DiskImage.cpp
index 1c8d0cf..024bf15 100644
--- a/Device/DiskImage.cpp
+++ b/Device/DiskImage.cpp
@@ -41,7 +41,7 @@ DiskImage::DiskImage(MappedFile *file)
     _file.adopt(*file);
 
     _blocks = 0;
-    _readOnly = file->readOnly();
+    _readOnly = _file.readOnly();
     _adaptor = NULL;
 }