diff --git a/src/data_source.c b/src/data_source.c
index 1bd1213..4dd6ad0 100644
--- a/src/data_source.c
+++ b/src/data_source.c
@@ -127,7 +127,7 @@ void ds_free_data(IsoDataSource *src)
     data = (struct file_data_src*)src->data;
 
     /* close the file if needed */
-    if (data->fd != 1) {
+    if (data->fd != -1) {
         close(data->fd);
     }
     free(data->path);