diff --git a/src/isolate.h b/src/isolate.h
index 4fb8272cf5..35443d79dd 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -1561,7 +1561,7 @@ class CodeTracer FINAL : public Malloced {
     }
 
     if (file_ == NULL) {
-      file_ = base::OS::FOpen(filename_.start(), "a");
+      file_ = base::OS::FOpen(filename_.start(), "ab");
     }
 
     scope_depth_++;