diff --git a/dcalc/PrimaDelayCalc.cc b/dcalc/PrimaDelayCalc.cc
index a5ea608c..a23d417f 100644
--- a/dcalc/PrimaDelayCalc.cc
+++ b/dcalc/PrimaDelayCalc.cc
@@ -590,6 +590,17 @@ PrimaDelayCalc::stampEqns()
   C_.setZero();
   B_.setZero();
 
+  // The stamps below insert into G_/C_ in parasitic traversal order, which is
+  // unrelated to the node indices assigned by findNodeCount(). coeffRef() on a
+  // packed sparse column has no free slot for an out of order insert, so it
+  // shifts the remaining values over, making stampEqns() quadratic in the node
+  // count. Reserving slack per column gives the inserts somewhere to land.
+  // Node degree in an RC network is small; stamp_slack covers the diagonal, the
+  // resistor and coupling capacitor off diagonals and the driver row.
+  constexpr int stamp_slack = 8;
+  G_.reserve(Eigen::VectorXi::Constant(order_, stamp_slack));
+  C_.reserve(Eigen::VectorXi::Constant(order_, stamp_slack));
+
   NetSet drvr_nets(network_);
   for (ArcDcalcArg &dcalc_arg : *dcalc_args_) {
     const Net *net = dcalc_arg.drvrNet(network_);