diff --git a/liberty/Liberty.cc b/liberty/Liberty.cc
index de019009..da8fe383 100644
--- a/liberty/Liberty.cc
+++ b/liberty/Liberty.cc
@@ -2761,7 +2761,7 @@ LibertyPort::clkTreeDelay(float in_slew,
         || (arc_set->role() == TimingRole::clockTreePathMax()
             && min_max == MinMax::max())) {
       const TimingArc *arc = arc_set->arcTo(to_rf);
-      if (arc->fromEdge()->asRiseFall() == from_rf) {
+      if (arc && arc->fromEdge()->asRiseFall() == from_rf) {
         const GateTableModel *gate_model = dynamic_cast<GateTableModel*>(arc->model());
         if (gate_model)
           return gate_model->delayModel()->findValue(in_slew, 0.0, 0.0);
diff --git a/spice/test/spice_write.ok b/spice/test/spice_write.ok
index 29fd8697..1b2d81a5 100644
--- a/spice/test/spice_write.ok
+++ b/spice/test/spice_write.ok
@@ -24,6 +24,4 @@ Path Type: max
            9.92   slack (MET)
 
 
-Differences found at line 2.
-.include "/workspace/sta/OpenSTA/spice/test/results/spice_out/mock_model.sp"
-.include "/workspace/sta2/OpenSTA/spice/test/results/spice_out/mock_model.sp"
+No differences found.
diff --git a/spice/test/spice_write.tcl b/spice/test/spice_write.tcl
index fe82163c..e9712268 100644
--- a/spice/test/spice_write.tcl
+++ b/spice/test/spice_write.tcl
@@ -47,4 +47,4 @@ write_path_spice \
   -model_file $model_file \
   -power VDD \
   -ground VSS
-diff_files $test_name.spok [file join $spice_dir path_1.sp]
+diff_files $test_name.spok [file join $spice_dir path_1.sp] "mock_model.sp"