diff --git a/src/io.cpp b/src/io.cpp
index b938fb5c..e0b91af7 100644
--- a/src/io.cpp
+++ b/src/io.cpp
@@ -329,7 +329,7 @@ void IO::output_obj(const OutputFeaturesPtr& allFeatures) {
     std::vector<std::ofstream> of;
     std::vector<std::string>   fs(numOutputSurfaces), bs(numOutputSurfaces);
 
-    std::vector<std::unordered_map<std::string, int>> dPts(numOutputSurfaces);
+    std::vector<std::unordered_map<std::string, unsigned long>> dPts(numOutputSurfaces);
     //-- Output points
 //    int count = 0; // to output each building as a separate group
     for (auto& f : allFeatures) {
@@ -441,7 +441,7 @@ void IO::output_cityjson(const OutputFeaturesPtr& allFeatures) {
 void IO::get_obj_pts(const Mesh& mesh,
                      std::string& fs,
                      std::string& bs,
-                     std::unordered_map<std::string, int>& dPts) {
+                     std::unordered_map<std::string, unsigned long>& dPts) {
     for (auto& face : mesh.faces()) {
         if (IO::is_degen(mesh, face)) continue;
         std::string bsTemp;
@@ -614,4 +614,4 @@ std::string IO::gen_key_bucket(const T& p) {
 }
 //- Explicit template instantiation
 template std::string IO::gen_key_bucket<Point_3>(const Point_3& p);
-template std::string IO::gen_key_bucket<Vector_3>(const Vector_3& p);
\ No newline at end of file
+template std::string IO::gen_key_bucket<Vector_3>(const Vector_3& p);
diff --git a/src/io.h b/src/io.h
index ac2df9e2..1d506bbc 100644
--- a/src/io.h
+++ b/src/io.h
@@ -48,7 +48,7 @@ namespace IO {
     void output_stl(const OutputFeaturesPtr& allFeatures);
     void output_cityjson(const OutputFeaturesPtr& allFeatures);
 
-    void get_obj_pts(const Mesh& mesh, std::string& fs, std::string& bs, std::unordered_map<std::string, int>& dPts);
+    void get_obj_pts(const Mesh& mesh, std::string& fs, std::string& bs, std::unordered_map<std::string, unsigned long>& dPts);
     void get_stl_pts(Mesh& mesh, std::string& fs);
     void get_cityjson_geom(const Mesh& mesh, nlohmann::json& g, std::unordered_map<std::string, int>& dPts, std::string primitive);
 
@@ -65,4 +65,4 @@ namespace IO {
     template <typename T> std::string gen_key_bucket(const T& p);
 }
 
-#endif //CITY4CFD_IO_H
\ No newline at end of file
+#endif //CITY4CFD_IO_H