diff --git a/bnpm/timeSeries.py b/bnpm/timeSeries.py
index 1a2f05f..401e8d0 100644
--- a/bnpm/timeSeries.py
+++ b/bnpm/timeSeries.py
@@ -65,6 +65,8 @@ def convolve_along_axis(
     '''
     tic = time.time()
 
+    axis = array.ndim + axis if axis<0 else axis  ## convert negative axis to positive axis
+
     if array.ndim == 1:
         multicore_pref = False
     if multicore_pref: