diff --git a/.github/workflows/build-cppfront.yaml b/.github/workflows/build-cppfront.yaml
index d1282924cd..c19564e98a 100644
--- a/.github/workflows/build-cppfront.yaml
+++ b/.github/workflows/build-cppfront.yaml
@@ -38,6 +38,9 @@ jobs:
           - runs-on: macos-latest
             compiler: clang++
             cxx-std: 'c++20'
+          - runs-on: ubuntu-22.04
+            compiler: clang++-15
+            cxx-std: 'c++20'
           - runs-on: ubuntu-24.04
             compiler: clang++-16
             cxx-std: 'c++20'
@@ -47,6 +50,9 @@ jobs:
           - runs-on: ubuntu-24.04
             compiler: clang++-18
             cxx-std: 'c++20'
+          - runs-on: ubuntu-24.04
+            compiler: clang++-18
+            cxx-std: 'c++2b'
           - runs-on: ubuntu-24.04
             compiler: g++-14
             cxx-std: 'c++2b'
diff --git a/source/parse.h b/source/parse.h
index 0c35215c80..9ff0033b79 100644
--- a/source/parse.h
+++ b/source/parse.h
@@ -141,6 +141,9 @@ struct primary_expression_node
     // Cache to work around <https://github.com/llvm/llvm-project/issues/73336>.
     bool expression_list_is_fold_expression = false;
 
+    // Out-of-line definition of the dtor is necessary due to the forward-declared
+    // type(s) used in a std::unique_ptr as a member
+    ~primary_expression_node();
 
     //  API
     //
@@ -234,6 +237,10 @@ struct prefix_expression_node
     std::vector<token const*> ops;
     std::unique_ptr<postfix_expression_node> expr;
 
+    // Out-of-line definition of the dtor is necessary due to the forward-declared
+    // type(s) used in a std::unique_ptr as a member
+    ~prefix_expression_node();
+
     //  API
     //
     auto is_fold_expression() const
@@ -293,6 +300,10 @@ struct binary_expression_node
 
     binary_expression_node();
 
+    // Out-of-line definition of the dtor is necessary due to the forward-declared
+    // type(s) used as Term in a std::unique_ptr as a member
+    ~binary_expression_node();
+
     struct term
     {
         token const* op;
@@ -1087,6 +1098,18 @@ struct template_argument
         std::unique_ptr<type_id_node>
     > arg;
 
+    // The type needs to be movable
+    // The copy ctor+operator are implicitly deleted due to the std::unique_ptr member
+    // Because a forward-declared type is used in a std::unique_ptr as a member an out-of-line dtor is necessary
+    // Because of the OOL dtor together with the fact that the copy ctor+operator are deleted
+    // the move ctor+operator need to be explicitly defaulted
+    // As a result the default constructor also needs to be explicitly defaulted
+    template_argument() = default;
+    template_argument(template_argument&&) = default;
+    template_argument& operator=(template_argument&&) = default;
+
+    ~template_argument();
+
     auto to_string() const
         -> std::string;
 };
@@ -1800,6 +1823,10 @@ struct iteration_statement_node
     std::unique_ptr<statement_node>             body;               // used for "for", else null
     bool                                        for_with_in = false;// used for "for," says whether loop variable is 'in'
 
+    // Out-of-line definition of the dtor is necessary due to the forward-declared
+    // type(s) used in a std::unique_ptr as a member
+    ~iteration_statement_node();
+
     auto position() const
         -> source_position
     {
@@ -1851,6 +1878,10 @@ struct alternative_node
     source_position                      equal_sign;
     std::unique_ptr<statement_node>      statement;
 
+    // Out-of-line definition of the dtor is necessary due to the forward-declared
+    // type(s) used in a std::unique_ptr as a member
+    ~alternative_node();
+
     auto position() const
         -> source_position
     {
@@ -1874,6 +1905,10 @@ struct inspect_expression_node
 
     std::vector<std::unique_ptr<alternative_node>> alternatives;
 
+    // Out-of-line definition of the dtor is necessary due to the forward-declared
+    // type(s) used in a std::unique_ptr as a member
+    ~inspect_expression_node();
+
     auto position() const
         -> source_position
     {
@@ -2011,6 +2046,10 @@ struct statement_node
 
     statement_node(compound_statement_node* compound_parent_ = nullptr);
 
+    // Out-of-line definition of the dtor is necessary due to the forward-declared
+    // type(s) used in a std::unique_ptr as a member
+    ~statement_node();
+
     enum active { expression=0, compound, selection, declaration, return_, iteration, using_, contract, inspect, jump };
     std::variant<
         std::unique_ptr<expression_statement_node>,
@@ -4386,6 +4425,26 @@ struct translation_unit_node
     }
 };
 
+// Definitions of out-of-line dtors for nodes with unique_ptr members of forward-declared types
+primary_expression_node::~primary_expression_node() = default;
+
+prefix_expression_node::~prefix_expression_node() = default;
+
+template<
+    String   Name,
+    typename Term
+>
+binary_expression_node<Name, Term>::~binary_expression_node() = default;
+
+alternative_node::~alternative_node() = default;
+
+iteration_statement_node::~iteration_statement_node() = default;
+
+template_argument::~template_argument() = default;
+
+inspect_expression_node::~inspect_expression_node() = default;
+
+statement_node::~statement_node() = default;
 
 //-----------------------------------------------------------------------
 //