diff --git a/src/node_map.cpp b/src/node_map.cpp
index e3acbeea7..2dd46e549 100644
--- a/src/node_map.cpp
+++ b/src/node_map.cpp
@@ -287,12 +287,13 @@ void NodeMap::renderFinished() {
 // Instance
 
 NodeMap::NodeMap(v8::Handle<v8::Object> source_) :
-    source(source_),
     view(sharedDisplay()),
     fs(*ObjectWrap::Unwrap<NodeFileSource>(source_)),
     map(view, fs, mbgl::Map::RenderMode::Still),
     async(new uv_async_t) {
 
+    NanAssignPersistent(source, source_);
+
     async->data = this;
     uv_async_init(uv_default_loop(), async, [](uv_async_t *as, int) {
         reinterpret_cast<NodeMap *>(as->data)->renderFinished();