diff --git a/src/slic3r/GUI/GLCanvas3D.cpp b/src/slic3r/GUI/GLCanvas3D.cpp
index 3fc090c6b..ceb59bea1 100644
--- a/src/slic3r/GUI/GLCanvas3D.cpp
+++ b/src/slic3r/GUI/GLCanvas3D.cpp
@@ -1383,7 +1383,7 @@ bool GLCanvas3D::Selection::is_single_full_instance() const
         return false;
 
     int object_idx = m_valid ? get_object_idx() : -1;
-    if ((object_idx < 0) || ((int)m_model->objects.size() < object_idx))
+    if ((object_idx < 0) || ((int)m_model->objects.size() <= object_idx))
         return false;
 
     int instance_idx = (*m_volumes)[*m_list.begin()]->instance_idx();