diff --git a/include/sta/Corner.hh b/include/sta/Corner.hh
index 9eef31fc..cdb472b8 100644
--- a/include/sta/Corner.hh
+++ b/include/sta/Corner.hh
@@ -108,7 +108,7 @@ public:
   PathAnalysisPt *findPathAnalysisPt(const MinMax *min_max) const;
   void addLiberty(LibertyLibrary *lib,
 		  const MinMax *min_max);
-  LibertySeq *libertyLibraries(const MinMax *min_max);
+  const LibertySeq &libertyLibraries(const MinMax *min_max) const;
   int libertyIndex(const MinMax *min_max) const;
 
 protected:
diff --git a/sdf/SdfWriter.cc b/sdf/SdfWriter.cc
index 016c95e3..506a3a86 100644
--- a/sdf/SdfWriter.cc
+++ b/sdf/SdfWriter.cc
@@ -215,24 +215,27 @@ SdfWriter::writeHeader(LibertyLibrary *default_lib,
     gzprintf(stream_, " (VERSION \"%s\")\n", STA_VERSION);
   gzprintf(stream_, " (DIVIDER %c)\n", sdf_divider_);
 
-  OperatingConditions *cond_min = 
-    sdc_->operatingConditions(MinMax::min());
-  if (cond_min == nullptr)
-    cond_min = default_lib->defaultOperatingConditions();
-  OperatingConditions *cond_max = 
-    sdc_->operatingConditions(MinMax::max());
-  if (cond_max == nullptr)
-    cond_max = default_lib->defaultOperatingConditions();
+  LibertyLibrary *lib_min = default_lib;
+  const LibertySeq &libs_min = corner_->libertyLibraries(MinMax::min());
+  if (!libs_min.empty())
+    lib_min = libs_min[0];
+  LibertyLibrary *lib_max = default_lib;
+  const LibertySeq &libs_max = corner_->libertyLibraries(MinMax::max());
+  if (!libs_max.empty())
+    lib_max = libs_max[0];
+
+  OperatingConditions *cond_min = lib_min->defaultOperatingConditions();
+  OperatingConditions *cond_max = lib_max->defaultOperatingConditions();
   if (cond_min && cond_max) {
     gzprintf(stream_, " (VOLTAGE %.3f::%.3f)\n",
-	     cond_min->voltage(),
-	     cond_max->voltage());
+             cond_min->voltage(),
+             cond_max->voltage());
     gzprintf(stream_, " (PROCESS \"%.3f::%.3f\")\n",
-	     cond_min->process(),
-	     cond_max->process());
+             cond_min->process(),
+             cond_max->process());
     gzprintf(stream_, " (TEMPERATURE %.3f::%.3f)\n",
-	     cond_min->temperature(),
-	     cond_max->temperature());
+             cond_min->temperature(),
+             cond_max->temperature());
   }
 
   const char *sdf_timescale = nullptr;
diff --git a/search/Corner.cc b/search/Corner.cc
index cda81d0e..e9abe7e0 100644
--- a/search/Corner.cc
+++ b/search/Corner.cc
@@ -467,10 +467,10 @@ Corner::addLiberty(LibertyLibrary *lib,
   liberty_[min_max->index()].push_back(lib);
 }
 
-LibertySeq *
-Corner::libertyLibraries(const MinMax *min_max)
+const LibertySeq &
+Corner::libertyLibraries(const MinMax *min_max) const
 {
-  return &liberty_[min_max->index()];
+  return liberty_[min_max->index()];
 }
 
 int