diff --git a/include/sta/TableModel.hh b/include/sta/TableModel.hh
index 31d4d165..b52a4805 100644
--- a/include/sta/TableModel.hh
+++ b/include/sta/TableModel.hh
@@ -497,7 +497,7 @@ public:
   const TableAxis *capAxis() const { return cap_axis_.get(); }
   // Make voltage wavefroms from liberty time/current values.
   // Required before voltageTime, timeVoltage, voltageCurrent.
-  void makeVoltageWaveforms(float vdd);
+  void ensureVoltageWaveforms(float vdd);
   float timeCurrent(float slew,
                     float cap,
                     float time);
diff --git a/liberty/Liberty.cc b/liberty/Liberty.cc
index 48e9b345..2b5f04e6 100644
--- a/liberty/Liberty.cc
+++ b/liberty/Liberty.cc
@@ -1948,7 +1948,7 @@ LibertyCell::ensureVoltageWaveforms(const DcalcAnalysisPtSeq &dcalc_aps)
           if (model) {
             OutputWaveforms *output_waveforms = model->outputWaveforms();
             if (output_waveforms)
-              output_waveforms->makeVoltageWaveforms(vdd);
+              output_waveforms->ensureVoltageWaveforms(vdd);
           }
         }
       }
diff --git a/liberty/TableModel.cc b/liberty/TableModel.cc
index 21786e63..fe430ef0 100644
--- a/liberty/TableModel.cc
+++ b/liberty/TableModel.cc
@@ -1664,17 +1664,19 @@ OutputWaveforms::checkAxes(const TableTemplate *tbl_template)
 }
 
 void
-OutputWaveforms::makeVoltageWaveforms(float vdd)
+OutputWaveforms::ensureVoltageWaveforms(float vdd)
 {
-  vdd_ = vdd;
-  size_t size = current_waveforms_.size();
-  voltage_waveforms_.resize(size);
-  voltage_currents_.resize(size);
-  size_t cap_count = cap_axis_->size();
-  for (size_t slew_index = 0; slew_index < slew_axis_->size(); slew_index++) {
-    for (size_t cap_index = 0; cap_index < cap_count; cap_index++) {
-      size_t wave_index = slew_index * cap_count + cap_index;
-      findVoltages(wave_index, cap_axis_->axisValue(cap_index));
+  if (voltage_waveforms_.empty()) {
+    vdd_ = vdd;
+    size_t size = current_waveforms_.size();
+    voltage_waveforms_.resize(size);
+    voltage_currents_.resize(size);
+    size_t cap_count = cap_axis_->size();
+    for (size_t slew_index = 0; slew_index < slew_axis_->size(); slew_index++) {
+      for (size_t cap_index = 0; cap_index < cap_count; cap_index++) {
+        size_t wave_index = slew_index * cap_count + cap_index;
+        findVoltages(wave_index, cap_axis_->axisValue(cap_index));
+      }
     }
   }
 }