diff --git a/pkgs/by-name/li/libmpeg2/getopt-getenv-signatures.patch b/pkgs/by-name/li/libmpeg2/getopt-getenv-signatures.patch
new file mode 100644
index 000000000000..881f11882371
--- /dev/null
+++ b/pkgs/by-name/li/libmpeg2/getopt-getenv-signatures.patch
@@ -0,0 +1,26 @@
+diff --git a/src/getopt.c b/src/getopt.c
+index 4744e43..19776f3 100644
+--- a/src/getopt.c
++++ b/src/getopt.c
+@@ -208,7 +208,7 @@ static char *posixly_correct;
+    whose names are inconsistent.  */
+ 
+ #ifndef getenv
+-extern char *getenv ();
++extern char *getenv (const char *);
+ #endif
+ 
+ static char *
+diff --git a/src/getopt.h b/src/getopt.h
+index b0147e9..6f1e784 100644
+--- a/src/getopt.h
++++ b/src/getopt.h
+@@ -133,7 +133,7 @@ struct option
+    errors, only prototype getopt for the GNU C library.  */
+ extern int getopt (int __argc, char *const *__argv, const char *__shortopts);
+ # else /* not __GNU_LIBRARY__ */
+-extern int getopt ();
++extern int getopt (int, char *const*, const char *);
+ # endif /* __GNU_LIBRARY__ */
+ 
+ # ifndef __need_getopt
diff --git a/pkgs/by-name/li/libmpeg2/package.nix b/pkgs/by-name/li/libmpeg2/package.nix
index 7860056707ca..4242f5c2edd5 100644
--- a/pkgs/by-name/li/libmpeg2/package.nix
+++ b/pkgs/by-name/li/libmpeg2/package.nix
@@ -13,6 +13,11 @@ stdenv.mkDerivation rec {
     sha256 = "1m3i322n2fwgrvbs1yck7g5md1dbg22bhq5xdqmjpz5m7j4jxqny";
   };
 
+  patches = [
+    # Fixes mismatching definitions with C23 / GCC15 on non-glibc platforms
+    ./getopt-getenv-signatures.patch
+  ];
+
   # Otherwise clang fails with 'duplicate symbol ___sputc'
   buildFlags = lib.optional stdenv.hostPlatform.isDarwin "CFLAGS=-std=gnu89";