diff --git a/liberty/LibertyWriter.cc b/liberty/LibertyWriter.cc
index 87792688..6d6a7b80 100644
--- a/liberty/LibertyWriter.cc
+++ b/liberty/LibertyWriter.cc
@@ -273,6 +273,8 @@ LibertyWriter::writeCell(const LibertyCell *cell)
     fprintf(stream_, "    area : %.3f \n", area);
   if (cell->isMacro())
     fprintf(stream_, "    is_macro : true;\n");
+  if (cell->interfaceTiming())
+    fprintf(stream_, "    interface_timing : true;\n");
 
   LibertyCellPortIterator port_iter(cell);
   while (port_iter.hasNext()) {
diff --git a/search/MakeTimingModel.cc b/search/MakeTimingModel.cc
index fa168456..6cbae47e 100644
--- a/search/MakeTimingModel.cc
+++ b/search/MakeTimingModel.cc
@@ -153,6 +153,7 @@ void
 MakeTimingModel::makeCell()
 {
   cell_ = lib_builder_->makeCell(library_, cell_name_, filename_);
+  cell_->setInterfaceTiming(true);
 }
 
 void