diff --git a/README.md b/README.md
index 9828c113..dceed0be 100644
--- a/README.md
+++ b/README.md
@@ -83,7 +83,6 @@ If you execute `cmake` with debug flag `-DCMAKE_BUILD_TYPE=Debug`, it builds the
 Picrin scheme depends on some external libraries to build the binary:
 
 - perl
-- lex (preferably, flex)
 - getopt
 - libedit (optional)
 - regex.h of POSIX.1 (optional)
diff --git a/docs/deploy.rst b/docs/deploy.rst
index 3c8b9ceb..0807466b 100644
--- a/docs/deploy.rst
+++ b/docs/deploy.rst
@@ -64,7 +64,6 @@ Requirement
 Picrin scheme depends on some external libraries to build the binary:
 
 - perl
-- lex (preferably, flex)
 - getopt
 - readline (optional)
 - regex.h of POSIX.1 (optional)