diff --git a/src/libslic3r/Config.hpp b/src/libslic3r/Config.hpp
index 7698bf5cf..d38612b59 100644
--- a/src/libslic3r/Config.hpp
+++ b/src/libslic3r/Config.hpp
@@ -721,7 +721,10 @@ public:
                 this->values[i] = rhs_vec->values[i];
                 modified        = true;
             } else {
-                this->values[i] = default_value[default_index[i]-1];
+                if ((i < default_index.size()) && (default_index[i] - 1 < default_value.size()))
+                    this->values[i] = default_value[default_index[i] - 1];
+                else
+                    this->values[i] = default_value[0];
             }
         }
         return modified;