diff --git a/src/vpp-api/python/vpp_papi.py b/src/vpp-api/python/vpp_papi.py
index 7b66c0f..67ac22a 100644
--- a/src/vpp-api/python/vpp_papi.py
+++ b/src/vpp-api/python/vpp_papi.py
@@ -360,6 +360,7 @@
                         size += v[1].size
             else:
                 if callable(v):
+                    size = 0
                     (s, l) = v(self, False, buf, off, None)
                     res.append(l)
                     size += s