diff --git a/lasp/filter/filterbank_design.py b/lasp/filter/filterbank_design.py
index f935dac..4b5552d 100644
--- a/lasp/filter/filterbank_design.py
+++ b/lasp/filter/filterbank_design.py
@@ -259,7 +259,7 @@ class FilterBankDesigner:
         for x in self.xs:
             xl = x
             fl = self.fl(x)
-            if self.fl(x+1) > freq[0]:
+            if fl >= freq[0]:
                 break
 
         # Find upper frequency xu