diff --git a/src/draco/io/mesh_io.cc b/src/draco/io/mesh_io.cc
index adc66e5..24160ac 100644
--- a/src/draco/io/mesh_io.cc
+++ b/src/draco/io/mesh_io.cc
@@ -31,7 +31,8 @@ std::unique_ptr<Mesh> ReadMeshFromFile(const std::string &file_name,
   std::unique_ptr<Mesh> mesh(new Mesh());
   // Analyze file extension.
   const std::string extension =
-      parser::ToLower(file_name.substr(file_name.size() - 4));
+      parser::ToLower(file_name.size() >= 4 ?
+      file_name.substr(file_name.size() - 4) : file_name);
   if (extension == ".obj") {
     // Wavefront OBJ file format.
     ObjDecoder obj_decoder;
diff --git a/src/draco/io/point_cloud_io.cc b/src/draco/io/point_cloud_io.cc
index 548da35..d3435a3 100644
--- a/src/draco/io/point_cloud_io.cc
+++ b/src/draco/io/point_cloud_io.cc
@@ -25,7 +25,8 @@ std::unique_ptr<PointCloud> ReadPointCloudFromFile(
     const std::string &file_name) {
   std::unique_ptr<PointCloud> pc(new PointCloud());
   // Analyze file extension.
-  const std::string extension = file_name.substr(file_name.size() - 4);
+  const std::string extension = file_name.size() >= 4 ?
+      file_name.substr(file_name.size() - 4) : file_name;
   if (extension == ".obj") {
     // Wavefront OBJ file format.
     ObjDecoder obj_decoder;
diff --git a/src/draco/tools/draco_decoder.cc b/src/draco/tools/draco_decoder.cc
index 4f3bac0..512301b 100644
--- a/src/draco/tools/draco_decoder.cc
+++ b/src/draco/tools/draco_decoder.cc
@@ -134,8 +134,8 @@ int main(int argc, char **argv) {
 
   // Save the decoded geometry into a file.
   // TODO(ostava): Currently only .ply and .obj are supported.
-  const std::string extension =
-      options.output.substr(options.output.size() - 4);
+  const std::string extension = options.output.size() >= 4 ?
+      options.output.substr(options.output.size() - 4) : options.output;
   if (extension == ".obj") {
     draco::ObjEncoder obj_encoder;
     if (mesh) {