diff -Naurp1 a/common.mk b/common.mk
--- a/common.mk	2020-10-01 18:15:38.000000000 +0600
+++ b/common.mk	2020-11-24 20:43:21.849455472 +0600
@@ -1028,4 +1028,3 @@ realclean-srcs-ext::
 
-EXTRA_SRCS = $(srcdir)/ext/json/parser/parser.c \
-	     $(srcdir)/ext/date/zonetab.h \
+EXTRA_SRCS = $(srcdir)/ext/date/zonetab.h \
 	     $(empty)
@@ -1142,6 +1141,2 @@ $(srcdir)/ext/ripper/ripper.c: $(srcdir)
 
-$(srcdir)/ext/json/parser/parser.c: $(srcdir)/ext/json/parser/parser.rl $(srcdir)/ext/json/parser/prereq.mk
-	$(ECHO) generating $@
-	$(Q) $(CHDIR) $(@D) && $(exec) $(MAKE) -f prereq.mk $(mflags) \
-		Q=$(Q) ECHO=$(ECHO) top_srcdir=../../.. srcdir=. VPATH=../../.. BASERUBY="$(BASERUBY)"
 
diff -Naurp1 a/doc/maintainers.rdoc b/doc/maintainers.rdoc
--- a/doc/maintainers.rdoc	2020-10-01 18:15:38.000000000 +0600
+++ b/doc/maintainers.rdoc	2020-11-24 20:44:01.216453644 +0600
@@ -312,6 +312,2 @@ Zachary Scott (zzak)
   https://rubygems.org/gems/io-console
-[ext/json]
-  NARUSE, Yui (naruse), Hiroshi SHIBATA (hsbt)
-  https://github.com/flori/json
-  https://rubygems.org/gems/json
 [ext/openssl]
diff -Naurp1 a/ext/.document b/ext/.document
--- a/ext/.document	2020-10-01 18:15:38.000000000 +0600
+++ b/ext/.document	2020-11-24 20:44:30.082452304 +0600
@@ -29,5 +29,2 @@ io/nonblock/nonblock.c
 io/wait/wait.c
-json/generator/generator.c
-json/lib
-json/parser/parser.c
 nkf/lib
diff -Naurp1 a/ext/Setup b/ext/Setup
--- a/ext/Setup	2020-10-01 18:15:38.000000000 +0600
+++ b/ext/Setup	2020-11-24 20:45:09.336450482 +0600
@@ -22,5 +22,2 @@
 #io/wait
-#json
-#json/generator
-#json/parser
 #nkf
diff -Naurp1 a/LEGAL b/LEGAL
--- a/LEGAL	2020-10-01 18:15:38.000000000 +0600
+++ b/LEGAL	2020-11-24 20:40:30.975463405 +0600
@@ -659,27 +659,2 @@ ext/digest/sha2/sha2.h::
 
-ext/json/generator/generator.c::
-
-  The file contains the following copyright notice.
-
-  >>>
-    Copyright 2001-2004 Unicode, Inc.
-
-    Disclaimer::
-
-      This source code is provided as is by Unicode, Inc. No claims are
-      made as to fitness for any particular purpose. No warranties of any
-      kind are expressed or implied. The recipient agrees to determine
-      applicability of information provided. If this file has been
-      purchased on magnetic or optical media from Unicode, Inc., the
-      sole remedy for any claim will be exchange of defective media
-      within 90 days of receipt.
-
-    Limitations on Rights to Redistribute This Code::
-
-      Unicode, Inc. hereby grants the right to freely use the information
-      supplied in this file in the creation of products supporting the
-      Unicode Standard, and to make copies of this file in any form
-      for internal or external distribution as long as this notice
-      remains attached.
-
 ext/nkf/nkf-utf8/config.h::
