diff --git a/ext/json/parser/parser.c b/ext/json/parser/parser.c
index 2d13bccf7e..fb10491d14 100644
--- a/ext/json/parser/parser.c
+++ b/ext/json/parser/parser.c
@@ -1,3 +1,4 @@
+/* This file is automatically generated from parser.rl by using ragel */
 
 #line 1 "parser.rl"
 #include "../fbuffer/fbuffer.h"
diff --git a/ext/json/parser/prereq.mk b/ext/json/parser/prereq.mk
index be7bcb4319..386999ba9d 100644
--- a/ext/json/parser/prereq.mk
+++ b/ext/json/parser/prereq.mk
@@ -5,6 +5,7 @@ RAGEL = ragel
 .rl.c:
 	$(RAGEL) -G2 $<
 	$(BASERUBY) -pli -e '$$_.sub!(/[ \t]+$$/, "")' \
-	-e '$$_.sub!(/^static const int (JSON_.*=.*);$$/, "enum {\\1};")' $@
+	-e '$$_.sub!(/^static const int (JSON_.*=.*);$$/, "enum {\\1};")' \
+	-e '$$header ||= $$_ = "/* This file is automatically generated from parser.rl by using ragel */\n" + $$_' $@
 
 parser.c: