diff --git a/lasp/filter/filterbank_design.py b/lasp/filter/filterbank_design.py
index 83a86d3..dabbaf9 100644
--- a/lasp/filter/filterbank_design.py
+++ b/lasp/filter/filterbank_design.py
@@ -256,7 +256,7 @@ 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