diff --git a/particle.py b/particle.py
index c3af2a8..ce562b3 100644
--- a/particle.py
+++ b/particle.py
@@ -152,7 +152,7 @@ class Particles:
             rp = self.attr['r'][ipart]+padding
             for pos in self.position_with_duplicates(ipart,padding=padding):
                 idxlo = np.array(fld.nearest_gridpoint(pos-rp,lower=True))
-                sfdim = np.ceil(2*rp/fld.spacing+1).astype('int')
+                sfdim = np.ceil(2*rp/fld.spacing+2).astype('int')
                 sf = fld.extract_subfield(idxlo,sfdim,deep=False,strict_bounds=False)
                 xsf = sf.x().reshape((-1,1,1))
                 ysf = sf.y().reshape((1,-1,1))