diff --git a/src/slic3r/GUI/GLModel.cpp b/src/slic3r/GUI/GLModel.cpp
index beebab47b..9bfcf87a3 100644
--- a/src/slic3r/GUI/GLModel.cpp
+++ b/src/slic3r/GUI/GLModel.cpp
@@ -175,7 +175,7 @@ void GLModel::set_color(int entity_id, const std::array<float, 4>& color)
     }
 }
 
-const std::array<float, 4> GLModel::get_color(int entity_id) const
+const std::array<float, 4> GLModel::get_color(size_t entity_id) const
 {
     if (entity_id < 0 || entity_id >= m_render_data.size()) return {};
     return m_render_data[entity_id].color;
diff --git a/src/slic3r/GUI/GLModel.hpp b/src/slic3r/GUI/GLModel.hpp
index eb592568d..cd30258f8 100644
--- a/src/slic3r/GUI/GLModel.hpp
+++ b/src/slic3r/GUI/GLModel.hpp
@@ -77,7 +77,7 @@ namespace GUI {
 
         // if entity_id == -1 set the color of all entities
         void set_color(int entity_id, const std::array<float, 4>& color);
-        const std::array<float, 4> get_color(int entity_id=0) const;
+        const std::array<float, 4> get_color(size_t entity_id = 0U) const;
 
         void reset();
         void render() const;