For gcc>=6 JSON_USE_INT64_DOUBLE_CONVERSION
diff --git a/include/json/config.h b/include/json/config.h
index 1b0581f..51027dd 100644
--- a/include/json/config.h
+++ b/include/json/config.h
@@ -114,6 +114,10 @@
 #define JSONCPP_DEPRECATED(message)
 #endif // if !defined(JSONCPP_DEPRECATED)
 
+#if __GNUC__ >= 6
+#  define JSON_USE_INT64_DOUBLE_CONVERSION 1
+#endif
+
 namespace Json {
 typedef int Int;
 typedef unsigned int UInt;