diff --git a/python/extras_pmt.py b/python/extras_pmt.py
index 84bec80..e71b4d5 100644
--- a/python/extras_pmt.py
+++ b/python/extras_pmt.py
@@ -45,7 +45,7 @@ def __pointer_to_ndarray(addr, nitems):
#re-create the blob data functions, but yield a numpy array instead
def pmt_blob_data(blob):
- return __pointer_to_ndarray(extras_swig.pmt_blob_rw_data(blob), extras_swig.pmt_blob_length(blob))
+ return __pointer_to_ndarray(extras_swig.pmt_blob_rw_data(blob), pmt.pmt_blob_length(blob))
#re-create mgr acquire by calling into python GIL-safe version
class pmt_mgr: