diff --git a/dssi-vst.cpp b/dssi-vst.cpp
index 0dfa95e..9118ef3 100644
--- a/dssi-vst.cpp
+++ b/dssi-vst.cpp
@@ -434,6 +434,8 @@ DSSIVSTPluginInstance::configure(std::string key, std::string value)
 		std::cerr << "DSSIVSTPluginInstance::configure: hide gui" << std::endl;
 		m_plugin->hideGUI();
 	    }
+	} else if (key == "DSSI_CUSTOMDATA_EXTENSION_KEY") {
+	    return "true";
 	}
     } catch (RemotePluginClosedException) {
 	m_ok = false;
diff --git a/dssi/dssi.h b/dssi/dssi.h
index 0911cc7..c31bd8b 100644
--- a/dssi/dssi.h
+++ b/dssi/dssi.h
@@ -170,6 +170,8 @@ typedef struct _DSSI_Descriptor {
     #define DSSI_GLOBAL_CONFIGURE_PREFIX "GLOBAL:"
     #define DSSI_PROJECT_DIRECTORY_KEY \
 	DSSI_RESERVED_CONFIGURE_PREFIX "PROJECT_DIRECTORY"
+    #define DSSI_CUSTOMDATA_EXTENSION_KEY \
+	DSSI_RESERVED_CONFIGURE_PREFIX "SUPPORTS_CUSTOMDATA"
 
     /**
      * get_program()