diff --git a/src/libslic3r/Model.cpp b/src/libslic3r/Model.cpp
index fd814976a5..a88bdd9910 100644
--- a/src/libslic3r/Model.cpp
+++ b/src/libslic3r/Model.cpp
@@ -1686,7 +1686,7 @@ bool model_volume_list_changed(const ModelObject &model_object_old, const ModelO
     return false;
 }
 
-#ifdef _DEBUG
+#ifndef NDEBUG
 // Verify whether the IDs of Model / ModelObject / ModelVolume / ModelInstance / ModelMaterial are valid and unique.
 void check_model_ids_validity(const Model &model)
 {
@@ -1732,6 +1732,6 @@ void check_model_ids_equal(const Model &model1, const Model &model2)
         }
     }
 }
-#endif /* _DEBUG */
+#endif /* NDEBUG */
 
 }
diff --git a/src/libslic3r/Model.hpp b/src/libslic3r/Model.hpp
index 0ae238510e..ba109246a5 100644
--- a/src/libslic3r/Model.hpp
+++ b/src/libslic3r/Model.hpp
@@ -629,11 +629,11 @@ extern bool model_object_list_extended(const Model &model_old, const Model &mode
 // than the old ModelObject.
 extern bool model_volume_list_changed(const ModelObject &model_object_old, const ModelObject &model_object_new, const ModelVolume::Type type);
 
-#ifdef _DEBUG
+#ifndef NDEBUG
 // Verify whether the IDs of Model / ModelObject / ModelVolume / ModelInstance / ModelMaterial are valid and unique.
 void check_model_ids_validity(const Model &model);
 void check_model_ids_equal(const Model &model1, const Model &model2);
-#endif /* _DEBUG */
+#endif /* NDEBUG */
 
 }