diff --git a/sigal/gallery.py b/sigal/gallery.py
index a214743..a1e7be8 100644
--- a/sigal/gallery.py
+++ b/sigal/gallery.py
@@ -51,10 +51,11 @@ class Gallery:
     def build_paths(self):
         "Build the list of directories with images"
 
-        self.paths = {}
+        self.paths = {'paths_list': []}
 
         for path, dirnames, filenames in os.walk(self.input_dir):
             relpath = os.path.relpath(path, self.input_dir)
+            self.paths['paths_list'].append(relpath)
 
             # sort images and sub-albums by name
             filenames.sort(key=str.lower)
@@ -95,8 +96,9 @@ class Gallery:
         self.build_paths()
         check_or_create_dir(self.output_dir)
 
-        # loop on directories
-        for path in self.paths.keys():
+        # loop on directories in reversed order, to process subdirectories
+        # before their parent
+        for path in reversed(self.paths['paths_list']):
             imglist = [os.path.join(self.input_dir, path, f)
                        for f in self.paths[path]['img']]
 
diff --git a/tests/test_gallery.py b/tests/test_gallery.py
index 52d9f2f..4645cc5 100644
--- a/tests/test_gallery.py
+++ b/tests/test_gallery.py
@@ -29,7 +29,10 @@ class TestGallery(unittest.TestCase):
     def test_filelist(self):
         paths = self.gal.paths
 
-        self.assertItemsEqual(paths.keys(), ['.', 'dir1', 'dir2', 'dir1/test'])
+        self.assertItemsEqual(paths.keys(),
+                              ['paths_list', '.', 'dir1', 'dir2', 'dir1/test'])
+        self.assertListEqual(paths['paths_list'],
+                             ['.', 'dir1', 'dir1/test', 'dir2'])
 
         self.assertListEqual(paths['.']['img'], [])
         self.assertItemsEqual(paths['.']['subdir'], ['dir1', 'dir2'])