diff --git a/pkgs/development/tools/analysis/radare2/default.nix b/pkgs/development/tools/analysis/radare2/default.nix
index cf31badfb3fc..61ac7bbfe464 100644
--- a/pkgs/development/tools/analysis/radare2/default.nix
+++ b/pkgs/development/tools/analysis/radare2/default.nix
@@ -81,9 +81,9 @@ stdenv.mkDerivation rec {
 
   # TODO: remove when upstream fixes the issue
   # https://github.com/radareorg/radare2/issues/22793
-  NIX_CFLAGS_COMPILE = lib.optionals stdenv.isDarwin [
+  env.NIX_CFLAGS_COMPILE = toString (lib.optionals stdenv.isDarwin [
      "-DTHREAD_CONVERT_THREAD_STATE_TO_SELF=1"
-  ];
+  ]);
 
   enableParallelBuilding = true;
   depsBuildBuild = [ buildPackages.stdenv.cc ];