diff --git a/liberty/Liberty.cc b/liberty/Liberty.cc
index c87093fb..ecf81f24 100644
--- a/liberty/Liberty.cc
+++ b/liberty/Liberty.cc
@@ -1175,7 +1175,8 @@ LibertyCell::isBuffer() const
   bufferPorts(input, output);
   return input && output
     && hasBufferFunc(input, output)
-    && !is_level_shifter_;
+    && !is_level_shifter_
+    && !is_pad_;
 }
 
 bool
@@ -1195,7 +1196,9 @@ LibertyCell::isInverter() const
   LibertyPort *output;
   bufferPorts(input, output);
   return input && output
-    && hasInverterFunc(input, output);
+    && hasInverterFunc(input, output)
+    && !is_level_shifter_
+    && !is_pad_;
 }
 
 bool