diff --git a/pkgs/tools/networking/nfstrace/default.nix b/pkgs/tools/networking/nfstrace/default.nix
index 50654da54e4f..72a0ea3682b7 100644
--- a/pkgs/tools/networking/nfstrace/default.nix
+++ b/pkgs/tools/networking/nfstrace/default.nix
@@ -22,9 +22,9 @@ stdenv.mkDerivation rec {
   nativeBuildInputs = [ cmake ];
 
   # To build with GCC 8+ it needs:
-  CXXFLAGS = [ "-Wno-class-memaccess" "-Wno-ignored-qualifiers" ];
+  CXXFLAGS = "-Wno-class-memaccess -Wno-ignored-qualifiers";
   # CMake can't find json_c without:
-  NIX_CFLAGS_COMPILE = [ "-I${json_c.dev}/include/json-c" ];
+  NIX_CFLAGS_COMPILE = "-I${json_c.dev}/include/json-c";
 
   doCheck = false; # requires network access