diff --git a/pkgs/by-name/uc/ucspi-tcp/package.nix b/pkgs/by-name/uc/ucspi-tcp/package.nix
index d12828e15847..27dd43811476 100644
--- a/pkgs/by-name/uc/ucspi-tcp/package.nix
+++ b/pkgs/by-name/uc/ucspi-tcp/package.nix
@@ -10,6 +10,9 @@ stdenv.mkDerivation rec {
   pname = "ucspi-tcp";
   version = "0.88";
 
+  # Uses K&R C style function declarations which GCC 14+ rejects
+  env.NIX_CFLAGS_COMPILE = "-std=gnu89";
+
   src = fetchurl {
     url = "https://cr.yp.to/ucspi-tcp/ucspi-tcp-${version}.tar.gz";
     sha256 = "171yl9kfm8w7l17dfxild99mbf877a9k5zg8yysgb1j8nz51a1ja";