diff --git a/preprocessor/ModFile.cc b/preprocessor/ModFile.cc
index 77805bc161c4bacd392532bf4be15dfe65cc1d4d..130e6da3d21479d0b078a952112f81c6d3a1395b 100644
--- a/preprocessor/ModFile.cc
+++ b/preprocessor/ModFile.cc
@@ -1271,7 +1271,8 @@ ModFile::writeJsonOutput(const string &basename, JsonOutputPointType json, JsonF
     symbol_table.freeze();
 
   if (json_output_mode == standardout)
-    cout << "{" << endl;
+    cout << "//-- BEGIN JSON --// " << endl
+         << "{" << endl;
 
   writeJsonOutputParsingCheck(basename, json_output_mode, json == transformpass, json == computingpass);
 
@@ -1282,7 +1283,8 @@ ModFile::writeJsonOutput(const string &basename, JsonOutputPointType json, JsonF
     writeJsonComputingPassOutput(basename, json_output_mode, jsonderivsimple);
 
   if (json_output_mode == standardout)
-    cout << "}" << endl;
+    cout << "}" << endl
+         << "//-- END JSON --// " << endl;
 
   switch (json)
     {