diff --git a/dcalc/LumpedCapDelayCalc.cc b/dcalc/LumpedCapDelayCalc.cc
index bb748a82..91c38bab 100644
--- a/dcalc/LumpedCapDelayCalc.cc
+++ b/dcalc/LumpedCapDelayCalc.cc
@@ -16,6 +16,8 @@
 
 #include "LumpedCapDelayCalc.hh"
 
+#include <cmath>  // isnan
+
 #include "Debug.hh"
 #include "Units.hh"
 #include "TimingArc.hh"
@@ -29,6 +31,8 @@
 
 namespace sta {
 
+using std::isnan;
+
 ArcDelayCalc *
 makeLumpedCapDelayCalc(StaState *sta)
 {