diff --git a/producer/api/python/asapo_producer.pyx.in b/producer/api/python/asapo_producer.pyx.in
index ba9a5a837725b2ef9c1f6824de7b838d297578cb..89eb6ca142775e333c47c526bceadfc3707d34c4 100644
--- a/producer/api/python/asapo_producer.pyx.in
+++ b/producer/api/python/asapo_producer.pyx.in
@@ -103,7 +103,7 @@ cdef void* data_pointer(data) except? NULL:
     cdef const unsigned char[::1] memview = reshaped_view
     return <void*>&memview[0]
 
-cdef int data_nbytes(data) except -1:
+def data_nbytes(data):
     if data is None:
         return 0
     return memoryview(data).nbytes