diff --git a/src/slic3r/GUI/GCodeViewer.cpp b/src/slic3r/GUI/GCodeViewer.cpp
index 36ac85df94..bd4653ab8f 100644
--- a/src/slic3r/GUI/GCodeViewer.cpp
+++ b/src/slic3r/GUI/GCodeViewer.cpp
@@ -697,7 +697,9 @@ void GCodeViewer::init()
             buffer.render_primitive_type = TBuffer::ERenderPrimitiveType::Line;
             buffer.vertices.format = VBuffer::EFormat::Position;
 #if ENABLE_GL_CORE_PROFILE
-            buffer.shader = OpenGLManager::get_gl_info().is_core_profile() ? "dashed_thick_lines" : "flat";
+            // on MAC using the geometry shader of dashed_thick_lines is too slow
+            buffer.shader = "flat";
+//            buffer.shader = OpenGLManager::get_gl_info().is_core_profile() ? "dashed_thick_lines" : "flat";
 #else
             buffer.shader = "flat";
 #endif // ENABLE_GL_CORE_PROFILE