diff --git a/byaccj-c99.patch b/byaccj-c99.patch
new file mode 100644
index 0000000000000000000000000000000000000000..0fd17f9edd45ee7694433e54e1d09e7792a9e2cc
--- /dev/null
+++ b/byaccj-c99.patch
@@ -0,0 +1,17 @@
+Include <unistd.h> for the unlink function.  This avoids an implicit
+function declaration, increasing C99 compatibility.
+
+Submitted upstream: <https://sourceforge.net/p/byaccj/patches/5/>
+
+diff --git a/src/main.c b/src/main.c
+index 54b5e05ba3aa2946..e4deacd47a3c0d34 100755
+--- a/src/main.c
++++ b/src/main.c
+@@ -4,6 +4,7 @@
+ 
+ #ifndef __WIN32__  /*rwj  --  make portable*/
+ #include <signal.h>
++#include <unistd.h>
+ #else
+ #include <dir.h>
+ #endif
diff --git a/byaccj.spec b/byaccj.spec
index 577a37612457218aab261783e03c7a5ce40445c2..4781a5d6d15ebce2c2b0c2f3840163f90717de1c 100644
--- a/byaccj.spec
+++ b/byaccj.spec
@@ -1,11 +1,12 @@
 Name:		byaccj
 Version:	1.15
-Release:	22
+Release:	23
 Summary:	BYACC/J Java extension
 License:	Public Domain
 URL:		http://byaccj.sourceforge.net/
 Source0:	http://sourceforge.net/projects/byaccj/files/byaccj/1.15/byaccj1.15_src.tar.gz
 Patch0:         fix-add-the-compilation-option-pie.patch
+Patch1:         byaccj-c99.patch
 
 BuildRequires:  make gdb-headless gcc
 
@@ -49,6 +50,9 @@ install -p -m 755 src/yacc %{buildroot}%{_bindir}/%{name}
 %doc docs/* src/README
 
 %changelog
+* Thu Feb 20 2025 pengjian <pengjian23@mails.ucas.ac.cn> - 1.15-23
+- C99 compatibility fix
+
 * Mon Aug 26 2024 wangqiang <wangqiang1@kylinos.cn> - 1.15-22
 - Support build with clang