diff --git a/libs/ardour/ardour/vst3_host.h b/libs/ardour/ardour/vst3_host.h
index afc4755f2a..5ccb53d9f3 100644
--- a/libs/ardour/ardour/vst3_host.h
+++ b/libs/ardour/ardour/vst3_host.h
@@ -343,7 +343,7 @@ protected:
 	std::vector<Vst::Event> _events;
 };
 
-class LIBARDOUR_LOCAL RAMStream : public IBStream
+class LIBARDOUR_LOCAL RAMStream : public IBStream, public ISizeableStream, public Vst::IStreamAttributes
 {
 public:
 	RAMStream ();
@@ -352,7 +352,7 @@ public:
 
 	virtual ~RAMStream ();
 
-	QUERY_INTERFACE_IMPL (IBStream)
+	tresult PLUGIN_API queryInterface (const TUID _iid, void** obj) SMTG_OVERRIDE;
 	uint32 PLUGIN_API addRef () SMTG_OVERRIDE { return 1; }
 	uint32 PLUGIN_API release () SMTG_OVERRIDE { return 1; }
 
@@ -362,6 +362,14 @@ public:
 	tresult PLUGIN_API seek  (int64 pos, int32 mode, int64* result) SMTG_OVERRIDE;
 	tresult PLUGIN_API tell  (int64* pos) SMTG_OVERRIDE;
 
+	/* ISizeableStream API */
+	tresult PLUGIN_API getStreamSize (int64&) SMTG_OVERRIDE;
+	tresult PLUGIN_API setStreamSize (int64) SMTG_OVERRIDE;
+
+	/* IStreamAttributes API */
+	tresult PLUGIN_API getFileName (Vst::String128 name) SMTG_OVERRIDE;
+	Vst::IAttributeList* PLUGIN_API getAttributes () SMTG_OVERRIDE;
+
 	/* convenience API for state I/O */
 	void rewind () { _pos = 0; }
 	bool readonly () const { return _readonly; }
@@ -404,6 +412,8 @@ private:
 	int64    _alloc;
 	int64    _pos;
 	bool     _readonly;
+
+	HostAttributeList attribute_list;
 };
 
 #if defined(__clang__)
diff --git a/libs/ardour/vst3_host.cc b/libs/ardour/vst3_host.cc
index 58cca6c724..507e22a6f1 100644
--- a/libs/ardour/vst3_host.cc
+++ b/libs/ardour/vst3_host.cc
@@ -35,6 +35,7 @@ DEF_CLASS_IID (IPluginFactory)
 DEF_CLASS_IID (IPluginFactory2)
 DEF_CLASS_IID (IPlugFrame)
 DEF_CLASS_IID (IPlugView)
+DEF_CLASS_IID (ISizeableStream)
 DEF_CLASS_IID (Vst::IAttributeList)
 DEF_CLASS_IID (Vst::IAudioProcessor)
 DEF_CLASS_IID (Vst::IAutomationState)
@@ -54,6 +55,7 @@ DEF_CLASS_IID (Vst::IParameterChanges)
 DEF_CLASS_IID (Vst::IParamValueQueue)
 DEF_CLASS_IID (Vst::IPlugInterfaceSupport)
 DEF_CLASS_IID (Vst::IProgramListData)
+DEF_CLASS_IID (Vst::IStreamAttributes)
 DEF_CLASS_IID (Vst::IUnitData)
 DEF_CLASS_IID (Vst::IUnitInfo)
 
@@ -510,6 +512,20 @@ RAMStream::~RAMStream ()
 	free (_data);
 }
 
+tresult
+RAMStream::queryInterface (const TUID _iid, void** obj)
+{
+  QUERY_INTERFACE (_iid, obj, FUnknown::iid, IBStream)
+  QUERY_INTERFACE (_iid, obj, IBStream::iid, IBStream)
+  QUERY_INTERFACE (_iid, obj, FUnknown::iid, ISizeableStream)
+  QUERY_INTERFACE (_iid, obj, ISizeableStream::iid, ISizeableStream)
+  QUERY_INTERFACE (_iid, obj, FUnknown::iid, Vst::IStreamAttributes)
+  QUERY_INTERFACE (_iid, obj, Vst::IStreamAttributes::iid, Vst::IStreamAttributes)
+
+  *obj = nullptr;
+  return kNoInterface;
+}
+
 bool
 RAMStream::reallocate_buffer (int64 size, bool exact)
 {
@@ -748,6 +764,34 @@ RAMStream::read_TUID (TUID& tuid)
 	return true;
 }
 
+tresult
+RAMStream::getStreamSize (int64& size)
+{
+	size = _alloc;
+	return kResultTrue;
+}
+
+tresult
+RAMStream::setStreamSize (int64 size)
+{
+	if (_readonly) {
+		return kResultFalse;
+	}
+	return reallocate_buffer (size, true) ? kResultOk : kOutOfMemory;
+}
+
+tresult
+RAMStream::getFileName (Vst::String128 name)
+{
+	return kNotImplemented;
+}
+
+Vst::IAttributeList*
+RAMStream::getAttributes ()
+{
+	return &attribute_list;
+}
+
 #ifndef NDEBUG
 
 #include <iostream>