diff --git a/src/brep/step_export.cpp b/src/brep/step_export.cpp
index b6ae7e0..eb97af2 100644
--- a/src/brep/step_export.cpp
+++ b/src/brep/step_export.cpp
@@ -3,6 +3,7 @@
 #include "vde/curves/nurbs_surface.h"
 #include <sstream>
 #include <fstream>
+#include <map>
 #include <cmath>
 
 namespace vde::brep {
@@ -226,7 +227,8 @@ struct StepWriter {
         auto& cp = surf.control_points();
         auto& w = surf.weights();
         int du = surf.degree_u(), dv = surf.degree_v();
-        auto& ku = surf.knots_u(), kv = surf.knots_v();
+        const auto& ku = surf.knots_u();
+        const auto& kv = surf.knots_v();
 
         // Control points list (row-major)
         std::stringstream cpts_ss;
diff --git a/src/brep/step_import.cpp b/src/brep/step_import.cpp
index 54555c8..0abb53b 100644
--- a/src/brep/step_import.cpp
+++ b/src/brep/step_import.cpp
@@ -1232,7 +1232,8 @@ private:
         }
 
         const auto& ent = entities_.at(ref);
-        curves::NurbsCurve nc;
+        // Default-construct with dummy line (NurbsCurve has no default ctor)
+        curves::NurbsCurve nc({Point3D(0,0,0), Point3D(1,0,0)}, {0,0,1,1}, {1,1}, 1);
         try {
             if (ent.type == "LINE")
                 nc = build_line_curve(ref);