diff --git a/include/tphrase/Generator.h b/include/tphrase/Generator.h
index 21805e7..67b372d 100644
--- a/include/tphrase/Generator.h
+++ b/include/tphrase/Generator.h
@@ -356,12 +356,12 @@ namespace tphrase {
         /** The function used by Generator.
             \return An instance of a type not to be published for the library users.
         */
-        DataSyntax &&move_syntax_data();
+        DataSyntax &&move_syntax_data() &&;
 
         /** The function used by Generator.
             \return The error messages that have been generated after creating the instance or clearing the previous error messages.
         */
-        std::string &&move_error_message();
+        std::string &&move_error_message() &&;
 
     private:
         struct Impl;
diff --git a/src/Generator.cpp b/src/Generator.cpp
index 5672550..331b71f 100644
--- a/src/Generator.cpp
+++ b/src/Generator.cpp
@@ -100,9 +100,9 @@ namespace tphrase {
     }
 
     Generator::Generator(Syntax &&syntax, const std::string &start_condition)
-        : pimpl{new Impl{syntax.move_error_message()}}
+        : pimpl{new Impl{std::move(syntax).move_error_message()}}
     {
-        pimpl->data.add(syntax.move_syntax_data(),
+        pimpl->data.add(std::move(syntax).move_syntax_data(),
                         start_condition,
                         pimpl->err_msg);
     }
@@ -175,8 +175,8 @@ namespace tphrase {
     bool Generator::add(Syntax &&syntax, const std::string &start_condition)
     {
         const std::size_t prev_len{pimpl->err_msg.size()};
-        pimpl->err_msg += syntax.get_error_message();
-        if (!pimpl->data.add(syntax.move_syntax_data(),
+        pimpl->err_msg += std::move(syntax).move_error_message();
+        if (!pimpl->data.add(std::move(syntax).move_syntax_data(),
                              start_condition,
                              pimpl->err_msg)) {
             return false;
diff --git a/src/Syntax.cpp b/src/Syntax.cpp
index 9827b18..5fbe2b8 100644
--- a/src/Syntax.cpp
+++ b/src/Syntax.cpp
@@ -191,12 +191,12 @@ namespace tphrase {
         return pimpl->data;
     }
 
-    DataSyntax &&Syntax::move_syntax_data()
+    DataSyntax &&Syntax::move_syntax_data() &&
     {
         return std::move(pimpl->data);
     }
 
-    std::string &&Syntax::move_error_message()
+    std::string &&Syntax::move_error_message() &&
     {
         return std::move(pimpl->err_msg);
     }