diff --git a/cnorxz/core/lib/array_wrapper.cpp b/cnorxz/core/lib/array_wrapper.cpp
index 81b71a9..90c0868 100644
--- a/cnorxz/core/lib/array_wrapper.cpp
+++ b/cnorxz/core/lib/array_wrapper.cpp
@@ -12,7 +12,7 @@ int PyCxArrayB_init(PyCxArrayB* self, PyObject* args, PyObject* kwds)
     SizeT ext = 0;
     char* type = NULL;
 
-    if(not PyArg_ParseTupleAndKeywords(args, kwds, "s|k", kwlist, &type, &ext)){
+    if(not PyArg_ParseTupleAndKeywords(args, kwds, "|sk", kwlist, &type, &ext)){
 	return -1;
     }