diff --git a/src/lib_json/json_writer.cpp b/src/lib_json/json_writer.cpp
index 1c9b7a4..eea17b6 100644
--- a/src/lib_json/json_writer.cpp
+++ b/src/lib_json/json_writer.cpp
@@ -944,11 +944,17 @@ class StreamWriterBuilder {
   CommentStyle cs_;
   std::string indentation_;
 public:
+  StreamWriterBuilder();
   virtual ~StreamWriterBuilder();
   virtual void setCommentStyle(CommentStyle cs);
   virtual void setIndentation(std::string indentation);
   virtual StreamWriter* newStreamWriter(std::ostream* sout) const;
 };
+StreamWriterBuilder::StreamWriterBuilder()
+  : cs_(CommentStyle::All)
+  , indentation_("\t")
+{
+}
 StreamWriterBuilder::~StreamWriterBuilder()
 {
 }