diff --git a/guest/vulkan_enc/ResourceTracker.cpp b/guest/vulkan_enc/ResourceTracker.cpp
index a197dc3..7a73c8a 100644
--- a/guest/vulkan_enc/ResourceTracker.cpp
+++ b/guest/vulkan_enc/ResourceTracker.cpp
@@ -1855,6 +1855,7 @@
 
     bool win32ExtMemAvailable = getHostDeviceExtensionIndex("VK_KHR_external_memory_win32") != -1;
     bool posixExtMemAvailable = getHostDeviceExtensionIndex("VK_KHR_external_memory_fd") != -1;
+    //TODO(b/349066492): this should check external_memory_metal extension when it's ready
     bool moltenVkExtAvailable = getHostDeviceExtensionIndex("VK_MVK_moltenvk") != -1;
     bool qnxExtMemAvailable =
         getHostDeviceExtensionIndex("VK_QNX_external_memory_screen_buffer") != -1;