diff --git a/qurator/modstool/altotool.py b/qurator/modstool/altotool.py
index 2bd73c1..66fac8c 100755
--- a/qurator/modstool/altotool.py
+++ b/qurator/modstool/altotool.py
@@ -79,7 +79,10 @@ def walk(m):
             if f.is_file() and not f.name.startswith('.'):
                 yield f.path
             elif f.is_dir():
-                yield from walk(f.path)
+                try:
+                    yield from walk(f.path)
+                except PermissionError:
+                    warnings.warn(f"Error walking {f.path}")
     else:
         yield m.path