diff --git a/libs/ardour/lv2_plugin.cc b/libs/ardour/lv2_plugin.cc
index 8c12a6b6b4..a8619d079d 100644
--- a/libs/ardour/lv2_plugin.cc
+++ b/libs/ardour/lv2_plugin.cc
@@ -1856,7 +1856,7 @@ LV2Plugin::write_to(RingBuffer<uint8_t>* dest,
 		return false;
 	}
 
-	uint8_t buf[buf_size];
+	uint8_t* buf = (uint8_t*) g_alloca (sizeof (uint8_t) * buf_size);
 	UIMessage* msg = (UIMessage*)&buf[0];
 	msg->index    = index;
 	msg->protocol = protocol;