diff --git a/src/csg/csg.cpp b/src/csg/csg.cpp
index 7de1dde17764f7320fee2353388e1f75c7c75bc3..72db8ad49fe8e42ebe60d96875e5fd94dc4cc67a 100644
--- a/src/csg/csg.cpp
+++ b/src/csg/csg.cpp
@@ -3,8 +3,8 @@
 #include <sstream>
 
 #include "csg.hpp"
-
 #include "csg_types.hpp"
+#include "csg_exception.hpp"
 
 namespace {
 
@@ -14,16 +14,22 @@ bool has_ext(std::string filename, std::string extension) {
   return filename.rfind(extension) == (filename.size() - extension.size());
 }
 
-std::optional<std::string> read_csg(std::string geom_file) {
+std::string read_csg(std::string geom_file) {
   if (!has_ext(geom_file, csg_ext)) {
-    std::cout << "Filename:  " << geom_file << "  must has extension .csg"
-              << std::endl;
-    return std::nullopt;
+     std::string err_msg = "ERROR:  Filename  " + geom_file + "  must have extension .csg";
+     std::cout << err_msg << std::endl;
+     throw csg::Exception("read_csg", err_msg);
   }
 
   std::ifstream in_stream;
   in_stream.open(geom_file.c_str());
 
+  if (!in_stream.good()) {
+     std::string err_msg = "ERROR:  Cannot open file   " + geom_file;
+     std::cout << err_msg << std::endl;
+     throw csg::Exception("read_csg", err_msg);
+  }
+
   std::stringstream str_stream;
   str_stream << in_stream.rdbuf();
   return str_stream.str();
@@ -62,21 +68,12 @@ double CsgIF::operator()(double xx, double yy, double zz) const noexcept {
 
 std::shared_ptr<csg::Tree> get_csgtree_from_filename(std::string geom_file) {
   auto csg_str = read_csg(geom_file);
-  if (!csg_str) {
-    std::cout << "Unable to read .csg file:  " << geom_file << std::endl;
-    return nullptr;
-  }
-  return csg::parse_csg(csg_str.value());
+  return csg::parse_csg(csg_str);
 }
 
 std::unique_ptr<CsgIF> get_csgif_from_filename(std::string geom_file) {
   auto csg_obj = get_csgtree_from_filename(geom_file);
 
-  if (!csg_obj) {
-    std::cout << "Failed to parse .csg file:  " << geom_file << std::endl;
-    return nullptr;
-  }
-
   csg::CsgIF csg_if(csg_obj);
   return std::make_unique<CsgIF>(csg_if);
 }
@@ -85,11 +82,6 @@ std::unique_ptr<CsgIF> get_csgif(const std::string &geom_file,
                                  bool is_internal_flow) {
   auto csg_obj = get_csgtree_from_filename(geom_file);
 
-  if (!csg_obj) {
-    std::cout << "Failed to parse .csg file:  " << geom_file << std::endl;
-    return nullptr;
-  }
-
   csg::CsgIF csg_if(csg_obj, is_internal_flow);
   return std::make_unique<CsgIF>(csg_if);
 }