diff --git a/liberty/TableModel.cc b/liberty/TableModel.cc
index 09f80ee8..676d29af 100644
--- a/liberty/TableModel.cc
+++ b/liberty/TableModel.cc
@@ -108,19 +108,18 @@ GateTableModel::gateDelay(const Pvt *pvt,
                           float &gate_delay,
                           float &drvr_slew) const
 {
-  if (delay_models_)
+  if (delay_models_ && delay_models_->model())
     gate_delay = findValue(pvt, delay_models_->model(), in_slew, load_cap, 0.0);
   else
     gate_delay = 0.0;
-  if (slew_models_)
+  if (slew_models_ && slew_models_->model()) {
     drvr_slew = findValue(pvt, slew_models_->model(), in_slew, load_cap, 0.0);
+    // Clip negative slews to zero.
+    if (drvr_slew < 0.0)
+      drvr_slew = 0.0;
+  }
   else
     drvr_slew = 0.0;
-  // Clip negative delays and slews to zero.
-  if (gate_delay < 0.0)
-    gate_delay = 0.0;
-  if (drvr_slew < 0.0)
-    drvr_slew = 0.0;
 }
 
 void