diff --git a/mrdna/segmentmodel.py b/mrdna/segmentmodel.py
index 7b97f930011eefedb8f49660d42ed05e9bf6352d..54e7f6e511f3830c5683e3bb516f1d84cd580b8d 100644
--- a/mrdna/segmentmodel.py
+++ b/mrdna/segmentmodel.py
@@ -1569,10 +1569,10 @@ class SegmentModel(ArbdModel):
         self.DEBUG = DEBUG
         if DEBUG > 0: print("Building ARBD Model")
         ArbdModel.__init__(self,segments,
-                           dimensions, origin,
-                           temperature, timestep, cutoff,
-                           decompPeriod, pairlistDistance=None,
-                           nonbondedResolution = 0,
+                           origin, dimensions,
+                           temperature, timestep, integrator, cutoff,
+                           decompPeriod, pairlist_distance=None,
+                           nonbonded_resolution = 0,
                            extra_bd_file_lines = extra_bd_file_lines
         )
 
@@ -1705,7 +1705,7 @@ class SegmentModel(ArbdModel):
 
         return twist_spring_from_lp(sep, Lp, self.temperature)
 
-    def extend(self, other, copy=True, include_strands=False):
+    def extend(self, other, copy=True, include_strands=True):
         assert( isinstance(other, SegmentModel) )
 
         try: