diff --git a/src/filesrc.c b/src/filesrc.c
index 302e6c7..9d94b44 100644
--- a/src/filesrc.c
+++ b/src/filesrc.c
@@ -20,7 +20,6 @@
 int iso_file_src_cmp(const void *n1, const void *n2)
 {
     const IsoFileSrc *f1, *f2;
-    int res;
     unsigned int fs_id1, fs_id2;
     dev_t dev_id1, dev_id2;
     ino_t ino_id1, ino_id2;
@@ -28,10 +27,8 @@ int iso_file_src_cmp(const void *n1, const void *n2)
     f1 = (const IsoFileSrc *)n1;
     f2 = (const IsoFileSrc *)n2;
 
-    res = iso_stream_get_id(f1->stream, &fs_id1, &dev_id1, &ino_id1);
-    res = iso_stream_get_id(f2->stream, &fs_id2, &dev_id2, &ino_id2);
-
-    //TODO take care about res <= 0
+    iso_stream_get_id(f1->stream, &fs_id1, &dev_id1, &ino_id1);
+    iso_stream_get_id(f2->stream, &fs_id2, &dev_id2, &ino_id2);
 
     if (fs_id1 < fs_id2) {
         return -1;
@@ -52,7 +49,7 @@ int iso_file_src_cmp(const void *n1, const void *n2)
 
 int iso_file_src_create(Ecma119Image *img, IsoFile *file, IsoFileSrc **src)
 {
-    int res;
+    int ret;
     IsoFileSrc *fsrc;
     unsigned int fs_id;
     dev_t dev_id;
@@ -62,35 +59,24 @@ int iso_file_src_create(Ecma119Image *img, IsoFile *file, IsoFileSrc **src)
         return ISO_NULL_POINTER;
     }
 
-    res = iso_stream_get_id(file->stream, &fs_id, &dev_id, &ino_id);
-    if (res < 0) {
-        return res;
-    } else if (res == 0) {
-        // TODO this corresponds to Stream that cannot provide a valid id
-        // Not implemented for now, but that shouldn't be here, the get_id
-        // above is not needed at all, the comparison function should take
-        // care of it
-        return ISO_ERROR;
-    } else {
-        int ret;
+    iso_stream_get_id(file->stream, &fs_id, &dev_id, &ino_id);
 
-        fsrc = malloc(sizeof(IsoFileSrc));
-        if (fsrc == NULL) {
-            return ISO_MEM_ERROR;
-        }
+    fsrc = malloc(sizeof(IsoFileSrc));
+    if (fsrc == NULL) {
+        return ISO_MEM_ERROR;
+    }
 
-        /* fill key and other atts */
-        fsrc->prev_img = file->msblock ? 1 : 0;
-        fsrc->block = file->msblock;
-        fsrc->sort_weight = file->sort_weight;
-        fsrc->stream = file->stream;
+    /* fill key and other atts */
+    fsrc->prev_img = file->msblock ? 1 : 0;
+    fsrc->block = file->msblock;
+    fsrc->sort_weight = file->sort_weight;
+    fsrc->stream = file->stream;
 
-        /* insert the filesrc in the tree */
-        ret = iso_rbtree_insert(img->files, fsrc, (void**)src);
-        if (ret <= 0) {
-            free(fsrc);
-            return ret;
-        }
+    /* insert the filesrc in the tree */
+    ret = iso_rbtree_insert(img->files, fsrc, (void**)src);
+    if (ret <= 0) {
+        free(fsrc);
+        return ret;
     }
     return ISO_SUCCESS;
 }
diff --git a/src/stream.c b/src/stream.c
index 417628c..3d12908 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -14,6 +14,8 @@
 #include <stdlib.h>
 #include <string.h>
 
+ino_t serial_id = (ino_t)1;
+
 typedef struct
 {
     IsoFileSource *src;
@@ -90,27 +92,18 @@ int fsrc_is_repeatable(IsoStream *stream)
 }
 
 static
-int fsrc_get_id(IsoStream *stream, unsigned int *fs_id, dev_t *dev_id,
+void fsrc_get_id(IsoStream *stream, unsigned int *fs_id, dev_t *dev_id,
                 ino_t *ino_id)
 {
     FSrcStreamData *data;
     IsoFilesystem *fs;
-
-    if (stream == NULL || fs_id == NULL || dev_id == NULL || ino_id == NULL) {
-        return ISO_NULL_POINTER;
-    }
+    
     data = (FSrcStreamData*)stream->data;
-
     fs = iso_file_source_get_filesystem(data->src);
 
     *fs_id = fs->get_id(fs);
-    if (fs_id == 0) {
-        return 0;
-    }
-
     *dev_id = data->dev_id;
     *ino_id = data->ino_id;
-    return ISO_SUCCESS;
 }
 
 static
@@ -178,9 +171,27 @@ int iso_file_source_stream_new(IsoFileSource *src, IsoStream **stream)
 
     /* take the ref to IsoFileSource */
     data->src = src;
-    data->dev_id = info.st_dev;
-    data->ino_id = info.st_ino;
     data->size = info.st_size;
+    
+    /* get the id numbers */
+    {
+        IsoFilesystem *fs;
+        unsigned int fs_id;
+        fs = iso_file_source_get_filesystem(data->src);
+
+        fs_id = fs->get_id(fs);
+        if (fs_id == 0) {
+            /* 
+             * the filesystem implementation is unable to provide valid
+             * st_dev and st_ino fields. Use serial_id.
+             */
+            data->dev_id = (dev_t) 0;
+            data->ino_id = serial_id++;
+        } else {
+            data->dev_id = info.st_dev;
+            data->ino_id = info.st_ino;
+        }
+    }
 
     str->refcount = 1;
     str->data = data;
diff --git a/src/stream.h b/src/stream.h
index 29a4b9d..70e2ef0 100644
--- a/src/stream.h
+++ b/src/stream.h
@@ -13,6 +13,13 @@
  */
 #include "fsource.h"
 
+/** 
+ * serial number to be used when you can't get a valid id for a Stream by other
+ * means. If you use this, both fs_id and dev_id should be set to 0.
+ * This must be incremented each time you get a reference to it.
+ */
+extern ino_t serial_id;
+
 /*
  * Some functions here will be moved to libisofs.h when we expose 
  * Streams.
@@ -70,14 +77,9 @@ typedef struct IsoStream_Iface
     int (*is_repeatable)(IsoStream *stream);
 
     /**
-     * Get an unique identifier for the IsoStream. If your implementation
-     * is unable to return a valid identifier, this function should return
-     * 0.
-     * 
-     * @return
-     *      1 on success, 0 if idenfier is not valid, < 0 error 
+     * Get an unique identifier for the IsoStream.
      */
-    int (*get_id)(IsoStream *stream, unsigned int *fs_id, dev_t *dev_id,
+    void (*get_id)(IsoStream *stream, unsigned int *fs_id, dev_t *dev_id,
                   ino_t *ino_id);
 
     /**
@@ -135,10 +137,10 @@ int iso_stream_is_repeatable(IsoStream *stream)
 }
 
 extern inline
-int iso_stream_get_id(IsoStream *stream, unsigned int *fs_id, dev_t *dev_id,
+void iso_stream_get_id(IsoStream *stream, unsigned int *fs_id, dev_t *dev_id,
                       ino_t *ino_id)
 {
-    return stream->class->get_id(stream, fs_id, dev_id, ino_id);
+    stream->class->get_id(stream, fs_id, dev_id, ino_id);
 }
 
 extern inline