diff --git a/pylot/core/pick/picker.py b/pylot/core/pick/picker.py
index 2355d4f3..03aa8577 100644
--- a/pylot/core/pick/picker.py
+++ b/pylot/core/pick/picker.py
@@ -244,7 +244,11 @@ class AICPicker(AutoPicker):
                               & (self.Tcf >= self.Pick)) # TODO: put this in a seperate function like getsignalwin
             # find maximum within slope determination window
             # 'cause slope should be calculated up to first local minimum only!
-            dataslope = self.Data[0].data[islope[0][0]:islope[0][len(islope[0]) - 1]]
+            try:
+                dataslope = self.Data[0].data[islope[0][0:-1]]
+            except IndexError:
+                print("Slope Calculation: empty array islope, check signal window")
+                return
             if len(dataslope) < 1:
                 print('No data in slope window found!')
                 return