diff --git a/ext/mini_racer_extension/mini_racer_extension.cc b/ext/mini_racer_extension/mini_racer_extension.cc
index 2fff58d..f60b675 100644
--- a/ext/mini_racer_extension/mini_racer_extension.cc
+++ b/ext/mini_racer_extension/mini_racer_extension.cc
@@ -1421,6 +1421,8 @@ rb_heap_snapshot(VALUE self, VALUE file) {
     FileOutputStream stream(fp);
     snap->Serialize(&stream, HeapSnapshot::kJSON);
 
+    fflush(fp);
+
     const_cast<HeapSnapshot*>(snap)->Delete();
 
     return Qtrue;