diff --git a/dcalc/GraphDelayCalc.cc b/dcalc/GraphDelayCalc.cc
index 9982f159..4f0729d9 100644
--- a/dcalc/GraphDelayCalc.cc
+++ b/dcalc/GraphDelayCalc.cc
@@ -116,6 +116,12 @@ GraphDelayCalc::ceff(Edge *,
   return 0.0;
 }
 
+bool
+GraphDelayCalc::isIdealClk(const Vertex *vertex)
+{
+  return false;
+}
+
 void
 GraphDelayCalc::minPulseWidth(const Pin *pin,
 			      const RiseFall *hi_low,
diff --git a/dcalc/GraphDelayCalc.hh b/dcalc/GraphDelayCalc.hh
index fc2186ec..c8707431 100644
--- a/dcalc/GraphDelayCalc.hh
+++ b/dcalc/GraphDelayCalc.hh
@@ -101,7 +101,7 @@ public:
   virtual float ceff(Edge *edge,
 		     TimingArc *arc,
 		     const DcalcAnalysisPt *dcalc_ap);
-  virtual bool isIdealClk(const Vertex *vertex) = 0;
+  virtual bool isIdealClk(const Vertex *vertex);
   // Precedence:
   //  SDF annotation
   //  Liberty library