diff --git a/src/gsi/gsi/gsiSerialisation.h b/src/gsi/gsi/gsiSerialisation.h
index fbe84d9b4..a9437c021 100644
--- a/src/gsi/gsi/gsiSerialisation.h
+++ b/src/gsi/gsi/gsiSerialisation.h
@@ -1799,6 +1799,8 @@ private:
   tl::Variant m_v;
 };
 
+#if __cplusplus >= 201703L
+
 /**
  *  @brief Specialization for std::optional
  */
@@ -1874,6 +1876,8 @@ private:
   std::optional<T> m_v;
 };
 
+#endif
+
 // ------------------------------------------------------------
 //  Vector adaptor framework
 
diff --git a/src/gsi/gsi/gsiTypes.h b/src/gsi/gsi/gsiTypes.h
index 6e5a3bc02..c7cbec2b1 100644
--- a/src/gsi/gsi/gsiTypes.h
+++ b/src/gsi/gsi/gsiTypes.h
@@ -439,7 +439,9 @@ template <> struct type_traits<__int128>                    : generic_type_trait
 template <> struct type_traits<double>                      : generic_type_traits<double_tag, double, T_double> { };
 template <> struct type_traits<float>                       : generic_type_traits<float_tag, float, T_float> { };
 template <> struct type_traits<std::string>                 : generic_type_traits<string_tag, StringAdaptor, T_string> { };
+#if __cplusplus >= 201703L
 template <typename T> struct type_traits<std::optional<T> > : generic_type_traits<var_tag, VariantAdaptor, T_var> { };
+#endif
 #if defined(HAVE_QT)
 template <> struct type_traits<QString>                     : generic_type_traits<string_tag, StringAdaptor, T_string> { };
 template <> struct type_traits<QStringRef>                  : generic_type_traits<string_tag, StringAdaptor, T_string> { };
@@ -479,7 +481,9 @@ template <> struct type_traits<const __int128 &>            : generic_type_trait
 template <> struct type_traits<const double &>              : generic_type_traits<double_cref_tag, double, T_double> { };
 template <> struct type_traits<const float &>               : generic_type_traits<float_cref_tag, float, T_float> { };
 template <> struct type_traits<const std::string &>         : generic_type_traits<string_cref_tag, StringAdaptor, T_string> { };
+#if __cplusplus >= 201703L
 template <typename T> struct type_traits<const std::optional<T> &>  : generic_type_traits<var_cref_tag, VariantAdaptor, T_var> { };
+#endif
 #if defined(HAVE_QT)
 template <> struct type_traits<const QString &>             : generic_type_traits<string_cref_tag, StringAdaptor, T_string> { };
 template <> struct type_traits<const QStringRef &>          : generic_type_traits<string_cref_tag, StringAdaptor, T_string> { };
@@ -516,7 +520,9 @@ template <> struct type_traits<__int128 &>                  : generic_type_trait
 template <> struct type_traits<double &>                    : generic_type_traits<double_ref_tag, double, T_double> { };
 template <> struct type_traits<float &>                     : generic_type_traits<float_ref_tag, float, T_float> { };
 template <> struct type_traits<std::string &>               : generic_type_traits<string_ref_tag, StringAdaptor, T_string> { };
+#if __cplusplus >= 201703L
 template <typename T> struct type_traits<std::optional<T> &>  : generic_type_traits<var_ref_tag, VariantAdaptor, T_var> { };
+#endif
 #if defined(HAVE_QT)
 template <> struct type_traits<QString &>                   : generic_type_traits<string_ref_tag, StringAdaptor, T_string> { };
 template <> struct type_traits<QStringRef &>                : generic_type_traits<string_ref_tag, StringAdaptor, T_string> { };
@@ -554,7 +560,9 @@ template <> struct type_traits<const __int128 *>            : generic_type_trait
 template <> struct type_traits<const double *>              : generic_type_traits<double_cptr_tag, double, T_double> { };
 template <> struct type_traits<const float *>               : generic_type_traits<float_cptr_tag, float, T_float> { };
 template <> struct type_traits<const std::string *>         : generic_type_traits<string_cptr_tag, StringAdaptor, T_string> { };
+#if __cplusplus >= 201703L
 template <typename T> struct type_traits<const std::optional<T> *>  : generic_type_traits<var_cptr_tag, VariantAdaptor, T_var> { };
+#endif
 #if defined(HAVE_QT)
 template <> struct type_traits<const QString *>             : generic_type_traits<string_cptr_tag, StringAdaptor, T_string> { };
 template <> struct type_traits<const QStringRef *>          : generic_type_traits<string_cptr_tag, StringAdaptor, T_string> { };
@@ -592,7 +600,9 @@ template <> struct type_traits<__int128 *>                  : generic_type_trait
 template <> struct type_traits<double *>                    : generic_type_traits<double_ptr_tag, double, T_double> { };
 template <> struct type_traits<float *>                     : generic_type_traits<float_ptr_tag, float, T_float> { };
 template <> struct type_traits<std::string *>               : generic_type_traits<string_ptr_tag, StringAdaptor, T_string> { };
+#if __cplusplus >= 201703L
 template <typename T> struct type_traits<std::optional<T> *>    : generic_type_traits<var_ptr_tag, VariantAdaptor, T_var> { };
+#endif
 #if defined(HAVE_QT)
 template <> struct type_traits<QString *>                   : generic_type_traits<string_ptr_tag, StringAdaptor, T_string> { };
 template <> struct type_traits<QStringRef *>                : generic_type_traits<string_ptr_tag, StringAdaptor, T_string> { };
diff --git a/src/gsi/gsi_test/gsiTest.h b/src/gsi/gsi_test/gsiTest.h
index f39bdf15f..73c462e0a 100644
--- a/src/gsi/gsi_test/gsiTest.h
+++ b/src/gsi/gsi_test/gsiTest.h
@@ -591,6 +591,7 @@ struct B
    */
   static tl::Variant new_b_by_variant ();
 
+#if __cplusplus >= 201703L
   /**
    *  @brief std::optional for simple and complex types
    */
@@ -609,7 +610,7 @@ struct B
   static int optional_a_ref_to_int (std::optional<A> &optional, int def)            { return optional_a_to_int (optional, def); }
   static int optional_a_cptr_to_int (const std::optional<A> *optional, int def)     { return optional_a_to_int (*optional, def); }
   static int optional_a_ptr_to_int (std::optional<A> optional, int def)             { return optional_a_to_int (*optional, def); }
-
+#endif
 
   std::string addr () const;