diff --git a/README.md b/README.md
index f34af0f..f6eacfe 100644
--- a/README.md
+++ b/README.md
@@ -240,17 +240,12 @@ GNU Coreutils is a collection of widely used utilities such as `cat`, `chmod`, `
 
 A few of the utilities cannot be easily compiled with Mes C library, so we skip them.
 
-#### Part 18: grep 2.4
-
-GNU `grep` is a pattern matching utility. Is is not immediately needed but will
-be useful later for autotools.
-
-#### Part 19: heirloom devtools
+#### Part 18: heirloom devtools
 `lex` and `yacc` from the Heirloom project. The Heirloom project is a collection
 of standard UNIX utilities derived from code by Caldera and Sun. Differently from
 the analogous utilities from the GNU project, they can be compiled with a simple `Makefile`.
 
-#### Part 20: bash 2.05b
+#### Part 19: bash 2.05b
 
 GNU `bash` is the most well known shell and the most complex piece of software
 so far. However, it comes with a number of great benefits over kaem, including
@@ -260,12 +255,12 @@ Bash ships with a bison pre-generated file here which we delete. Unfortunately,
 we have not bootstrapped bison but fortunately for us, heirloom yacc is able to
 cope here.
 
-#### Part 21: m4 1.4
+#### Part 20: m4 1.4.4
 
-`m4` is the first piece of software we need in the autotools suite. It allows
-macros to be defined and files to be generated from those macros.
+`m4` is the first piece of software we need in the autotools suite and flex 2.6.4.
+It allows macros to be defined and files to be generated from those macros.
 
-#### Part 22: flex 2.5.11
+#### Part 21: flex 2.5.11
 
 `flex` is a tool for generating lexers or scanners: programs that recognize lexical patters.
 
@@ -274,11 +269,7 @@ first flex 2.5.11 is compiled, with its scanner definition manually modified so
 it can be processed by lex for the Heirloom project (the required modifications
 are mostly syntactical, plus a few workarounds to avoid some flex advanced features).
 
-#### Part 23 flex 2.5.14
-
-Then we recompile unpatched `flex` using its own lexer.
-
-#### Part 24 musl 1.1.24
+#### Part 22 musl 1.1.24
 
 `musl` is a C standard library that is lightweight, fast, simple, free, and strives to be correct
 in the sense of standards-conformance and safety. `musl` is used by some distributions of GNU/Linux
@@ -289,8 +280,19 @@ newer or more complex programs.
 we replace all weak symbols with strong symbols and will patch `tcc` in the next step to ignore duplicate
 symbols.
 
-#### Part 25 tcc 0.9.27 (musl)
+#### Part 23 tcc 0.9.27 (musl)
 
 We recompile `tcc` against musl. This is a two stage process. First we build tcc-0.9.27 that itself
 links to Mes C library but produces binaries linked to musl. Then we recompile newly produced tcc
 with itself. Interestingly, tcc-0.9.27 linked against musl is self hosting.
+
+#### Part 24 flex 2.6.14
+
+We recompile unpatched GNU `flex` using older flex 2.5.11. This is again two stage process,
+first compile flex using scanner generated by old flex, then recompile scan.l using the new version
+of flex to remove any buggy artificats from the old flex.
+
+#### Part 25: grep 2.4
+
+GNU `grep` is a pattern matching utility. Is is not immediately needed but will
+be useful later for autotools.
diff --git a/rootfs.sh b/rootfs.sh
index 2d2cc45..5f61543 100755
--- a/rootfs.sh
+++ b/rootfs.sh
@@ -121,27 +121,27 @@ get_file ftp://sourceware.org/pub/bzip2/bzip2-1.0.8.tar.gz 1
 # coreutils 5.0
 get_file https://ftp.gnu.org/gnu/coreutils/coreutils-5.0.tar.bz2 1
 
-# grep 2.4
-get_file https://ftp.gnu.org/gnu/grep/grep-2.4.tar.gz
-
 # heirloom-devtools
 get_file http://downloads.sourceforge.net/project/heirloom/heirloom-devtools/070527/heirloom-devtools-070527.tar.bz2
 
 # bash 2.05b
 get_file https://ftp.gnu.org/pub/gnu/bash/bash-2.05b.tar.gz
 
-# m4 1.4
-get_file https://ftp.gnu.org/gnu/m4/m4-1.4.tar.gz
+# m4 1.4.4
+get_file https://ftp.gnu.org/gnu/m4/m4-1.4.4.tar.gz
 
 # flex 2.5.11
 get_file http://download.nust.na/pub2/openpkg1/sources/DST/flex/flex-2.5.11.tar.gz
 
-# flex 2.5.14
-get_file http://download.nust.na/pub2/openpkg1/sources/DST/flex/flex-2.5.14.tar.gz
-
 # musl 1.1.24
 get_file https://musl.libc.org/releases/musl-1.1.24.tar.gz
 
+# flex 2.6.4
+get_file https://github.com/westes/flex/releases/download/v2.6.4/flex-2.6.4.tar.gz
+
+# grep 2.4
+get_file https://ftp.gnu.org/gnu/grep/grep-2.4.tar.gz
+
 # General cleanup
 find tmp -name .git -exec rm -rf \;
 
diff --git a/sysa/after.kaem.run b/sysa/after.kaem.run
index f2a0ab1..db3a8d6 100755
--- a/sysa/after.kaem.run
+++ b/sysa/after.kaem.run
@@ -129,19 +129,13 @@ cd ${pkg}
 kaem --file ${pkg}.kaem
 cd ..
 
-# Part 18: grep
-pkg="grep-2.4"
-cd ${pkg}
-kaem --file ${pkg}.kaem
-cd ..
-
-# Part 19: heirloom-devtools
+# Part 18: heirloom-devtools
 pkg="heirloom-devtools-070527"
 cd ${pkg}
 kaem --file ${pkg}.kaem
 cd ..
 
-# Part 20: bash
+# Part 19: bash
 pkg="bash-2.05b"
 cd ${pkg}
 kaem --file ${pkg}.kaem
diff --git a/sysa/flex-2.5.11/flex-2.5.11.sh b/sysa/flex-2.5.11/flex-2.5.11.sh
index e96a2ce..c185150 100755
--- a/sysa/flex-2.5.11/flex-2.5.11.sh
+++ b/sysa/flex-2.5.11/flex-2.5.11.sh
@@ -1,13 +1,10 @@
 # When we rebuild flex it no longer needs patching
 # and can use simplified makefile
 src_prepare() {
-    if test -d /lex; then
-        default_src_prepare
-    else
-        cp ../../mk/main2.mk Makefile
-    fi
+    default_src_prepare
+
     touch config.h
-    rm parse.c parse.h scan.c
+    rm parse.c parse.h scan.c skel.c
 }
 
 src_install() {
diff --git a/sysa/flex-2.5.11/mk/main2.mk b/sysa/flex-2.5.11/mk/main2.mk
deleted file mode 100644
index 0f33808..0000000
--- a/sysa/flex-2.5.11/mk/main2.mk
+++ /dev/null
@@ -1,28 +0,0 @@
-CFLAGS = -DVERSION=\"2.5.11\"
-
-all: flex
-
-flex: ccl.o dfa.o ecs.o gen.o main.o misc.o nfa.o parse.o scan.o skel.o sym.o tblcmp.o yylex.o options.o scanopt.o buf.o
-	tcc -o $@ $^
-
-%.o: %.c
-	tcc -g -c $(CFLAGS) -o $@ $<
-
-scan.o: parse.h
-yylex.o: parse.h
-
-parse.c parse.h: parse.y
-	yacc -d parse.y
-	mv y.tab.h parse.h
-	mv y.tab.c parse.c
-
-scan.c: scan.l
-	flex scan.l
-	mv lex.yy.c scan.c
-
-skel.c: mkskel.sh flex.skl
-	/bin/sh ./mkskel.sh ./flex.skl > skel.c
-
-install: all
-	install flex $(PREFIX)/bin
-	ln -sf $(PREFIX)/bin/flex $(PREFIX)/bin/lex
diff --git a/sysa/flex-2.5.14/flex-2.5.14.sh b/sysa/flex-2.5.14/flex-2.5.14.sh
deleted file mode 100755
index edf31de..0000000
--- a/sysa/flex-2.5.14/flex-2.5.14.sh
+++ /dev/null
@@ -1,6 +0,0 @@
-src_prepare() {
-    default_src_prepare
-
-    touch config.h
-    rm parse.c parse.h scan.c
-}
diff --git a/sysa/flex-2.5.14/mk/main.mk b/sysa/flex-2.5.14/mk/main.mk
deleted file mode 100644
index caf85a2..0000000
--- a/sysa/flex-2.5.14/mk/main.mk
+++ /dev/null
@@ -1,29 +0,0 @@
-CFLAGS =    -I . \
-            -DVERSION=\"2.5.14\"
-
-all: flex
-
-flex: ccl.o dfa.o ecs.o gen.o main.o misc.o nfa.o parse.o scan.o skel.o sym.o tblcmp.o yylex.o options.o scanopt.o buf.o
-	tcc -o $@ $^
-
-%.o: %.c
-	tcc -g -c $(CFLAGS) -o $@ $<
-
-scan.o: parse.h
-yylex.o: parse.h
-
-parse.c parse.h: parse.y
-	yacc -d parse.y
-	mv y.tab.h parse.h
-	mv y.tab.c parse.c
-
-scan.c: scan.l
-	flex scan.l
-	mv lex.yy.c scan.c
-
-skel.c: mkskel.sh flex.skl
-	/bin/sh ./mkskel.sh ./flex.skl > skel.c
-
-install: all
-	install flex $(PREFIX)/bin
-	ln -sf $(PREFIX)/bin/flex $(PREFIX)/bin/lex
diff --git a/sysa/flex-2.5.14/src/.placeholder b/sysa/flex-2.5.14/src/.placeholder
deleted file mode 100644
index e69de29..0000000
diff --git a/sysa/flex-2.6.4/flex-2.6.4.sh b/sysa/flex-2.6.4/flex-2.6.4.sh
new file mode 100755
index 0000000..59737bb
--- /dev/null
+++ b/sysa/flex-2.6.4/flex-2.6.4.sh
@@ -0,0 +1,23 @@
+src_prepare() {
+    default_src_prepare
+
+    mv Makefile src/
+    touch src/config.h
+    rm src/parse.c src/parse.h src/scan.c src/skel.c
+}
+
+src_compile() {
+    cd src
+    default_src_compile
+    cd ..
+}
+
+src_install() {
+    cd src
+    default_src_install
+    cd ..
+
+    # Remove yacc, we won't need it any longer
+    rm ${PREFIX}/bin/yacc
+    rm /yaccpar
+}
diff --git a/sysa/flex-2.6.4/mk/main.mk b/sysa/flex-2.6.4/mk/main.mk
new file mode 100644
index 0000000..2064dab
--- /dev/null
+++ b/sysa/flex-2.6.4/mk/main.mk
@@ -0,0 +1,41 @@
+CC := tcc
+CFLAGS = -DVERSION=\"2.6.4\" \
+         -DM4=\"m4\" \
+         -DHAVE_LIMITS_H=1
+
+all: flex
+
+flex: buf.o ccl.o dfa.o ecs.o filter.o gen.o main.o misc.o nfa.o options.o parse.o regex.o scan.o scanflags.o scanopt.o skel.o sym.o tables.o tables_shared.o tblcmp.o yylex.o
+	$(CC) -o $@ $^ -lm
+
+flex-tmp: buf.o ccl.o dfa.o ecs.o filter.o gen.o main.o misc.o nfa.o options.o parse.o regex.o scan-tmp.o scanflags.o scanopt.o skel.o sym.o tables.o tables_shared.o tblcmp.o yylex.o
+	$(CC) -o $@ $^ -lm
+
+%.o: %.c
+	$(CC) $(CFLAGS) -g -c -I. -o $@ $<
+
+main.o: parse.h
+scan.o: parse.h
+scan-tmp.o: parse.h
+yylex.o: parse.h
+
+parse.c parse.h: parse.y
+	yacc -d parse.y
+	mv y.tab.h parse.h
+	mv y.tab.c parse.c
+	echo 'extern int yylval;' >> parse.h
+
+scan-tmp.c: scan.l
+	flex scan.l
+	mv lex.yy.c scan-tmp.c
+
+scan.c: scan.l flex-tmp
+	./flex-tmp scan.l
+	mv lex.yy.c scan.c
+
+skel.c: mkskel.sh flex.skl
+	/bin/sh ./mkskel.sh . m4 2.6.4 > skel.c
+
+install: all
+	install flex $(PREFIX)/bin
+	ln -sf $(PREFIX)/bin/flex $(PREFIX)/bin/lex
diff --git a/sysa/grep-2.4/grep-2.4.kaem b/sysa/grep-2.4/grep-2.4.kaem
deleted file mode 100755
index bf324e6..0000000
--- a/sysa/grep-2.4/grep-2.4.kaem
+++ /dev/null
@@ -1,23 +0,0 @@
-#!/bin/sh
-
-set -ex
-
-mkdir build
-cd build
-
-# Extract
-gunzip ../src/${pkg}.tar.gz
-tar xf ../src/${pkg}.tar
-cd ${pkg}
-cp ../../mk/main.mk Makefile
-
-# Build
-make
-
-# Install
-install grep /after/bin/
-
-# Test
-grep --version
-
-cd ../..
diff --git a/sysa/grep-2.4/mk/main.mk b/sysa/grep-2.4/mk/main.mk
index c35d91b..3a49d5e 100644
--- a/sysa/grep-2.4/mk/main.mk
+++ b/sysa/grep-2.4/mk/main.mk
@@ -8,7 +8,9 @@ AR      = tcc -ar
 CFLAGS  = -DPACKAGE=\"$(PACKAGE)\" \
           -DVERSION=\"$(VERSION)\" \
           -DHAVE_DIRENT_H=1 \
-          -DHAVE_UNISTD_H=1
+          -DHAVE_UNISTD_H=1 \
+          -DHAVE_STRERROR=1 \
+          -DREGEX_MALLOC=1
 
 .PHONY: all
 
@@ -19,3 +21,8 @@ all: grep
 
 grep: $(GREP_OBJECTS)
 	$(CC) $(CFLAGS) $^ $(LDFLAGS) -o $@
+
+install: all
+	install grep $(PREFIX)/bin
+	ln -sf $(PREFIX)/bin/grep $(PREFIX)/bin/egrep
+	ln -sf $(PREFIX)/bin/grep $(PREFIX)/bin/fgrep
diff --git a/sysa/m4-1.4/mk/main.mk b/sysa/m4-1.4.4/mk/main.mk
similarity index 83%
rename from sysa/m4-1.4/mk/main.mk
rename to sysa/m4-1.4.4/mk/main.mk
index a47d196..72c4176 100644
--- a/sysa/m4-1.4/mk/main.mk
+++ b/sysa/m4-1.4.4/mk/main.mk
@@ -7,7 +7,9 @@ AR      = tcc -ar
 
 CFLAGS  = -I lib \
           -DPRODUCT=\"$(PRODUCT)\" \
-          -DVERSION=\"$(VERSION)\"
+          -DVERSION=\"$(VERSION)\" \
+          -DHAVE_SIGNAL_H=1 \
+          -DPACKAGE_STRING=\"GNU\ M4\ 1.4.4\"
 
 LDFLAGS = -L . -lm4
 
diff --git a/sysa/m4-1.4/patches/signal-include.patch b/sysa/m4-1.4/patches/signal-include.patch
deleted file mode 100644
index c027475..0000000
--- a/sysa/m4-1.4/patches/signal-include.patch
+++ /dev/null
@@ -1,15 +0,0 @@
-sys/signal.h is not the POSIX appropriate place for signal.h, which mes libc
-attempts to conform to.
-
-diff -r -U3 src/m4.c src/m4.c
---- src/m4.c	1994-11-02 03:14:28.000000000 +0000
-+++ src/m4.c	2021-01-15 00:19:21.947654461 +0000
-@@ -19,7 +19,7 @@
- #include "m4.h"
- 
- #include <getopt.h>
--#include <sys/signal.h>
-+#include <signal.h>
- 
- static void usage _((int));
- 
diff --git a/sysa/run.sh b/sysa/run.sh
index f557e75..93b73c6 100755
--- a/sysa/run.sh
+++ b/sysa/run.sh
@@ -9,19 +9,22 @@ set -e
 
 export PREFIX=/after
 
-# Part 21
-build m4-1.4
+# Part 20
+build m4-1.4.4
 
-# Part 22
+# Part 21
 build flex-2.5.11
 
-# Part 23
-build flex-2.5.14
-
-# Part 24
+# Part 22
 build musl-1.1.24
 
-# Part 25
+# Part 23
 build tcc-0.9.27 tcc-musl.sh
 
+# Part 24
+build flex-2.6.4
+
+# Part 25
+build grep-2.4
+
 echo "Bootstrapping completed."