diff --git a/include/openPMD/IO/AbstractIOHandler.hpp b/include/openPMD/IO/AbstractIOHandler.hpp
index 220c8632c3..71a0587b0f 100644
--- a/include/openPMD/IO/AbstractIOHandler.hpp
+++ b/include/openPMD/IO/AbstractIOHandler.hpp
@@ -171,7 +171,7 @@ namespace internal
 
 namespace detail
 {
-    class BufferedActions;
+    struct BufferedActions;
 }
 
 /** Interface for communicating between logical and physically persistent data.
@@ -186,7 +186,7 @@ class AbstractIOHandler
 {
     friend class Series;
     friend class ADIOS2IOHandlerImpl;
-    friend class detail::BufferedActions;
+    friend struct detail::BufferedActions;
 
 private:
     IterationEncoding m_encoding = IterationEncoding::groupBased;
diff --git a/include/openPMD/backend/Writable.hpp b/include/openPMD/backend/Writable.hpp
index 5676266cb2..5e1272317e 100644
--- a/include/openPMD/backend/Writable.hpp
+++ b/include/openPMD/backend/Writable.hpp
@@ -52,7 +52,7 @@ namespace internal
 } // namespace internal
 namespace detail
 {
-    class BufferedActions;
+    struct BufferedActions;
 }
 
 /** @brief Layer to mirror structure of logical data and persistent data in