diff --git a/include/xo/type/array/IGCObject_DArrayType.hpp b/include/xo/type/array/IGCObject_DArrayType.hpp
index 55c58b5..28f0dcc 100644
--- a/include/xo/type/array/IGCObject_DArrayType.hpp
+++ b/include/xo/type/array/IGCObject_DArrayType.hpp
@@ -55,7 +55,7 @@ namespace xo {
             /** move instance using allocator **/
             static Opaque shallow_move(DArrayType & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
-            static size_type forward_children(DArrayType & self, obj<ACollector> gc) noexcept;
+            static void forward_children(DArrayType & self, obj<ACollector> gc) noexcept;
             ///@}
         };
 
diff --git a/include/xo/type/atomic/IGCObject_DAtomicType.hpp b/include/xo/type/atomic/IGCObject_DAtomicType.hpp
index 6907e7c..e5652bf 100644
--- a/include/xo/type/atomic/IGCObject_DAtomicType.hpp
+++ b/include/xo/type/atomic/IGCObject_DAtomicType.hpp
@@ -55,7 +55,7 @@ namespace xo {
             /** move instance using allocator **/
             static Opaque shallow_move(DAtomicType & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
-            static size_type forward_children(DAtomicType & self, obj<ACollector> gc) noexcept;
+            static void forward_children(DAtomicType & self, obj<ACollector> gc) noexcept;
             ///@}
         };
 
diff --git a/include/xo/type/function/IGCObject_DFunctionType.hpp b/include/xo/type/function/IGCObject_DFunctionType.hpp
index f43b41e..0c77e47 100644
--- a/include/xo/type/function/IGCObject_DFunctionType.hpp
+++ b/include/xo/type/function/IGCObject_DFunctionType.hpp
@@ -55,7 +55,7 @@ namespace xo {
             /** move instance using allocator **/
             static Opaque shallow_move(DFunctionType & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
-            static size_type forward_children(DFunctionType & self, obj<ACollector> gc) noexcept;
+            static void forward_children(DFunctionType & self, obj<ACollector> gc) noexcept;
             ///@}
         };
 
diff --git a/include/xo/type/list/IGCObject_DListType.hpp b/include/xo/type/list/IGCObject_DListType.hpp
index 296779e..322fc2d 100644
--- a/include/xo/type/list/IGCObject_DListType.hpp
+++ b/include/xo/type/list/IGCObject_DListType.hpp
@@ -55,7 +55,7 @@ namespace xo {
             /** move instance using allocator **/
             static Opaque shallow_move(DListType & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
-            static size_type forward_children(DListType & self, obj<ACollector> gc) noexcept;
+            static void forward_children(DListType & self, obj<ACollector> gc) noexcept;
             ///@}
         };
 
diff --git a/include/xo/type/typevar/IGCObject_DTypeVarRef.hpp b/include/xo/type/typevar/IGCObject_DTypeVarRef.hpp
index e491cc3..94be0f9 100644
--- a/include/xo/type/typevar/IGCObject_DTypeVarRef.hpp
+++ b/include/xo/type/typevar/IGCObject_DTypeVarRef.hpp
@@ -55,7 +55,7 @@ namespace xo {
             /** move instance using allocator **/
             static Opaque shallow_move(DTypeVarRef & self, obj<ACollector> gc) noexcept;
             /** during GC: forward immdiate children **/
-            static size_type forward_children(DTypeVarRef & self, obj<ACollector> gc) noexcept;
+            static void forward_children(DTypeVarRef & self, obj<ACollector> gc) noexcept;
             ///@}
         };
 
diff --git a/src/type/IGCObject_DArrayType.cpp b/src/type/IGCObject_DArrayType.cpp
index 34319c2..3186740 100644
--- a/src/type/IGCObject_DArrayType.cpp
+++ b/src/type/IGCObject_DArrayType.cpp
@@ -27,9 +27,9 @@ namespace xo {
             return self.shallow_move(gc);
         }
         auto
-        IGCObject_DArrayType::forward_children(DArrayType & self, obj<ACollector> gc) noexcept -> size_type
+        IGCObject_DArrayType::forward_children(DArrayType & self, obj<ACollector> gc) noexcept -> void
         {
-            return self.forward_children(gc);
+            self.forward_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/type/IGCObject_DAtomicType.cpp b/src/type/IGCObject_DAtomicType.cpp
index a0a9281..533f017 100644
--- a/src/type/IGCObject_DAtomicType.cpp
+++ b/src/type/IGCObject_DAtomicType.cpp
@@ -27,9 +27,9 @@ namespace xo {
             return self.shallow_move(gc);
         }
         auto
-        IGCObject_DAtomicType::forward_children(DAtomicType & self, obj<ACollector> gc) noexcept -> size_type
+        IGCObject_DAtomicType::forward_children(DAtomicType & self, obj<ACollector> gc) noexcept -> void
         {
-            return self.forward_children(gc);
+            self.forward_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/type/IGCObject_DFunctionType.cpp b/src/type/IGCObject_DFunctionType.cpp
index 04e5760..4a44fd3 100644
--- a/src/type/IGCObject_DFunctionType.cpp
+++ b/src/type/IGCObject_DFunctionType.cpp
@@ -27,9 +27,9 @@ namespace xo {
             return self.shallow_move(gc);
         }
         auto
-        IGCObject_DFunctionType::forward_children(DFunctionType & self, obj<ACollector> gc) noexcept -> size_type
+        IGCObject_DFunctionType::forward_children(DFunctionType & self, obj<ACollector> gc) noexcept -> void
         {
-            return self.forward_children(gc);
+            self.forward_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/type/IGCObject_DListType.cpp b/src/type/IGCObject_DListType.cpp
index fe721a3..7cabe58 100644
--- a/src/type/IGCObject_DListType.cpp
+++ b/src/type/IGCObject_DListType.cpp
@@ -27,9 +27,9 @@ namespace xo {
             return self.shallow_move(gc);
         }
         auto
-        IGCObject_DListType::forward_children(DListType & self, obj<ACollector> gc) noexcept -> size_type
+        IGCObject_DListType::forward_children(DListType & self, obj<ACollector> gc) noexcept -> void
         {
-            return self.forward_children(gc);
+            self.forward_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/type/IGCObject_DTypeVarRef.cpp b/src/type/IGCObject_DTypeVarRef.cpp
index f4f5d59..0dc4469 100644
--- a/src/type/IGCObject_DTypeVarRef.cpp
+++ b/src/type/IGCObject_DTypeVarRef.cpp
@@ -27,9 +27,9 @@ namespace xo {
             return self.shallow_move(gc);
         }
         auto
-        IGCObject_DTypeVarRef::forward_children(DTypeVarRef & self, obj<ACollector> gc) noexcept -> size_type
+        IGCObject_DTypeVarRef::forward_children(DTypeVarRef & self, obj<ACollector> gc) noexcept -> void
         {
-            return self.forward_children(gc);
+            self.forward_children(gc);
         }
 
     } /*namespace scm*/