diff --git a/pylot/core/pick/autopick.py b/pylot/core/pick/autopick.py
index 1c06bd7c..25a781b2 100644
--- a/pylot/core/pick/autopick.py
+++ b/pylot/core/pick/autopick.py
@@ -24,7 +24,7 @@ from pylot.core.util.utils import getPatternLine, gen_Pool, identifyPhase, loopI
 from obspy.taup import TauPyModel
 
 
-def autopickevent(data, param, iplot=0, fig_dict=None, ncores=1, metadata=None, origin=None):
+def autopickevent(data, param, iplot=0, fig_dict=None, ncores=0, metadata=None, origin=None):
     stations = []
     all_onsets = {}
     input_tuples = []
diff --git a/pylot/core/pick/picker.py b/pylot/core/pick/picker.py
index 67b114ce..f89d0036 100644
--- a/pylot/core/pick/picker.py
+++ b/pylot/core/pick/picker.py
@@ -397,8 +397,14 @@ class PragPicker(AutoPicker):
             # prominent trend: decrease aus
             # flat: use given aus
             cfdiff = np.diff(cfipick)
+            if len(cfdiff)<20:
+                print('PragPicker: Very few samples for CF. Check LTA window dimensions!')
             i0diff = np.where(cfdiff > 0)
             cfdiff = cfdiff[i0diff]
+            if len(cfdiff)<1:
+                print('PragPicker: Negative slope for CF. Check LTA window dimensions! STOP')
+                self.Pick = None
+                return
             minaus = min(cfdiff * (1 + self.aus))
             aus1 = max([minaus, self.aus])