diff --git a/python_src/lasp/filter/filterbank_design.py b/python_src/lasp/filter/filterbank_design.py
index 7ca0903..dfaccb8 100644
--- a/python_src/lasp/filter/filterbank_design.py
+++ b/python_src/lasp/filter/filterbank_design.py
@@ -209,6 +209,7 @@ class FilterBankDesigner:
         Returns:
             h: Linear filter transfer function [-]
         """
+        fs = self.fs
         fir = self.createFirFilter(fs, x)
 
         # Decimated sampling frequency [Hz]