diff --git a/dcalc/GraphDelayCalc.cc b/dcalc/GraphDelayCalc.cc
index 5b7af80b..b2d43242 100644
--- a/dcalc/GraphDelayCalc.cc
+++ b/dcalc/GraphDelayCalc.cc
@@ -47,6 +47,7 @@
 #include "Sdc.hh"
 #include "Scene.hh"
 #include "SearchPred.hh"
+#include "search/Sim.hh"
 #include "Stats.hh"
 #include "TimingArc.hh"
 #include "TimingRole.hh"
@@ -88,8 +89,10 @@ DcalcPred::searchFrom(const Vertex *from_vertex,
   const Pin *from_pin = from_vertex->pin();
   const Sdc *sdc = mode->sdc();
   const Network *network = sta_->network();
+  const Sim *sim = mode->sim();
   Net *net = network->net(from_pin);
   return !(sdc->isDisabledConstraint(from_pin)
+           || sim->isConstant(from_vertex)
 	   || (net && (network->isPower(net)
                        || network->isGround(net))));
 }
diff --git a/search/Sta.cc b/search/Sta.cc
index 7ece680a..a555e2ff 100644
--- a/search/Sta.cc
+++ b/search/Sta.cc
@@ -191,6 +191,7 @@ StaSimObserver::StaSimObserver(StaState *sta) :
 void
 StaSimObserver::valueChangeAfter(const Pin *pin)
 {
+  graph_delay_calc_->delayInvalid(pin);
   Vertex *vertex = graph_->pinDrvrVertex(pin);
   if (vertex) {
     search_->arrivalInvalid(vertex);
@@ -3676,8 +3677,10 @@ void
 Sta::delayCalcPreamble()
 {
   ensureLevelized();
-  for (Mode *mode : modes_)
+  for (Mode *mode : modes_) {
+    mode->sim()->ensureConstantsPropagated();
     mode->clkNetwork()->ensureClkNetwork();
+  }
 }
 
 void