diff --git a/libs/microbit/core.cpp b/libs/microbit/core.cpp
index 527460a4..c8cd2b24 100644
--- a/libs/microbit/core.cpp
+++ b/libs/microbit/core.cpp
@@ -183,6 +183,8 @@ namespace pxt {
   //%
   RefRecord* mkRecord(int reflen, int totallen);
   //%
+  RefRecord* mkClassInstance(int offset);
+  //%
   void debugMemLeaks();
   //%
   int incr(uint32_t e);
diff --git a/pxtarget.json b/pxtarget.json
index 2b5c0f04..de3d6af8 100644
--- a/pxtarget.json
+++ b/pxtarget.json
@@ -91,7 +91,7 @@
         "yottaTarget": "bbc-microbit-classic-gcc",
         "yottaCorePackage": "pxt-microbit-core",
         "githubCorePackage": "microsoft/pxt-microbit-core",
-        "gittag": "v0.4.1",
+        "gittag": "v0.4.2",
         "serviceId": "ws"
     },
     "serial": {