diff --git a/python_src/lasp/lasp_octavefilter.py b/python_src/lasp/lasp_octavefilter.py
index f8aeb43..78edcab 100644
--- a/python_src/lasp/lasp_octavefilter.py
+++ b/python_src/lasp/lasp_octavefilter.py
@@ -246,8 +246,8 @@ class SosFilterBank:
         for i, x in enumerate(self.xs):
             channel = self.designer.createSOSFilter(x)
             if sos is None:
-                sos = empty((channel.size, len(self.xs)))
-            sos[:, i] = channel.flatten() 
+                sos = np.empty((channel.size, len(self.xs)))
+            sos[:, i] = channel.flatten()
 
         self._fb = BiquadBank(sos)