diff --git a/liberty/TimingArc.cc b/liberty/TimingArc.cc
index cf9a7b74..17ad731b 100644
--- a/liberty/TimingArc.cc
+++ b/liberty/TimingArc.cc
@@ -240,11 +240,13 @@ TimingArcSet::addTimingArc(TimingArc *arc)
     criticalError(243, "timing arc max index exceeded\n");
   arcs_.push_back(arc);
 
-  int from_rf_index = arc->fromEdge()->asRiseFall()->index();
-  if (from_arc1_[from_rf_index] == nullptr)
-    from_arc1_[from_rf_index] = arc;
-  else if (from_arc2_[from_rf_index] == nullptr)
-    from_arc2_[from_rf_index] = arc;
+  if (arc->fromEdge()) {
+    int from_rf_index = arc->fromEdge()->asRiseFall()->index();
+    if (from_arc1_[from_rf_index] == nullptr)
+      from_arc1_[from_rf_index] = arc;
+    else if (from_arc2_[from_rf_index] == nullptr)
+      from_arc2_[from_rf_index] = arc;
+  }
 
   int to_rf_index = arc->toEdge()->asRiseFall()->index();
   to_arc_[to_rf_index] = arc;
@@ -476,8 +478,8 @@ timingArcsLess(const TimingArcSet *arc_set1,
        arc_itr1++, arc_itr2++) {
     const TimingArc *arc1 = *arc_itr1;
     const TimingArc *arc2 = *arc_itr2;
-    int from_index1 = arc1->fromEdge()->index();
-    int from_index2 = arc2->fromEdge()->index();
+    int from_index1 = arc1->fromEdge() ? arc1->fromEdge()->index() : -1;
+    int from_index2 = arc2->fromEdge() ? arc2->fromEdge()->index() : -1;
     if (from_index1 < from_index2)
       return true;
     if (from_index1 > from_index2)