diff --git a/pkgs/by-name/jo/john/package.nix b/pkgs/by-name/jo/john/package.nix
index b1dee316ce36..e1cbaef70ce0 100644
--- a/pkgs/by-name/jo/john/package.nix
+++ b/pkgs/by-name/jo/john/package.nix
@@ -40,6 +40,9 @@ stdenv.mkDerivation {
     })
   ];
 
+  # Fix build with gcc 15
+  env.NIX_CFLAGS_COMPILE = "-std=gnu17";
+
   postPatch = ''
     sed -ri -e '
       s!^(#define\s+CFG_[A-Z]+_NAME\s+).*/!\1"'"$out"'/etc/john/!