diff --git a/src/libslic3r/ExtrusionEntity.hpp b/src/libslic3r/ExtrusionEntity.hpp
index 98f0ebae1..7ca93baa6 100644
--- a/src/libslic3r/ExtrusionEntity.hpp
+++ b/src/libslic3r/ExtrusionEntity.hpp
@@ -511,12 +511,12 @@ inline void extrusion_entities_append_loops(ExtrusionEntitiesPtr &dst, Polygons
 class ExtrusionPrinter : public ExtrusionVisitorConst {
     std::stringstream ss;
 public:
-    virtual void use(const ExtrusionPath &path);
-    virtual void use(const ExtrusionPath3D &path3D);
-    virtual void use(const ExtrusionMultiPath &multipath);
-    virtual void use(const ExtrusionMultiPath3D &multipath);
-    virtual void use(const ExtrusionLoop &loop);
-    virtual void use(const ExtrusionEntityCollection &collection);
+    virtual void use(const ExtrusionPath &path) override;
+    virtual void use(const ExtrusionPath3D &path3D) override;
+    virtual void use(const ExtrusionMultiPath &multipath) override;
+    virtual void use(const ExtrusionMultiPath3D &multipath) override;
+    virtual void use(const ExtrusionLoop &loop) override;
+    virtual void use(const ExtrusionEntityCollection &collection) override;
     std::string str() { return ss.str(); }
     std::string print(const ExtrusionEntity &entity) && {
         entity.visit(*this);
diff --git a/src/libslic3r/SupportMaterial.cpp b/src/libslic3r/SupportMaterial.cpp
index cef90f25b..386a0a3b0 100644
--- a/src/libslic3r/SupportMaterial.cpp
+++ b/src/libslic3r/SupportMaterial.cpp
@@ -2674,15 +2674,15 @@ static std::string dbg_index_to_color(int idx)
 }
 #endif /* SLIC3R_DEBUG */
 
-class GetFirstPath : public ExtrusionVisitor {
+class GetFirstPath : public ExtrusionVisitorConst {
 public:
     const ExtrusionPath *extrusion_path_template = nullptr;
-    virtual void use(const ExtrusionPath &path) { extrusion_path_template = &path; }
-    virtual void use(const ExtrusionPath3D &path3D) { extrusion_path_template = &path3D; }
-    virtual void use(const ExtrusionMultiPath &multipath) { if (!multipath.paths.empty()) extrusion_path_template = &multipath.paths.front(); }
-    virtual void use(const ExtrusionMultiPath3D &multipath) { if (!multipath.paths.empty()) extrusion_path_template = &multipath.paths.front(); }
-    virtual void use(const ExtrusionLoop &loop) { if (!loop.paths.empty()) extrusion_path_template = &loop.paths.front(); }
-    virtual void use(const ExtrusionEntityCollection &collection) {
+    virtual void use(const ExtrusionPath &path) override { extrusion_path_template = &path; }
+    virtual void use(const ExtrusionPath3D &path3D) override { extrusion_path_template = &path3D; }
+    virtual void use(const ExtrusionMultiPath &multipath) override { if (!multipath.paths.empty()) extrusion_path_template = &multipath.paths.front(); }
+    virtual void use(const ExtrusionMultiPath3D &multipath) override { if (!multipath.paths.empty()) extrusion_path_template = &multipath.paths.front(); }
+    virtual void use(const ExtrusionLoop &loop) override { if (!loop.paths.empty()) extrusion_path_template = &loop.paths.front(); }
+    virtual void use(const ExtrusionEntityCollection &collection) override {
         auto it = collection.entities.begin();
         while (extrusion_path_template == nullptr && it != collection.entities.end()) {
             (*it)->visit(*this);