diff --git a/pkgs/applications/misc/keepassxc/default.nix b/pkgs/applications/misc/keepassxc/default.nix
index 1870c21bed13..3c74b6e91751 100644
--- a/pkgs/applications/misc/keepassxc/default.nix
+++ b/pkgs/applications/misc/keepassxc/default.nix
@@ -49,11 +49,11 @@ stdenv.mkDerivation rec {
     sha256 = "sha256-amedKK9nplLVJTldeabN3/c+g/QesrdH+qx+rba2/4s=";
   };
 
-  env.NIX_CFLAGS_COMPILE = lib.optionalString stdenv.cc.isClang [
+  env.NIX_CFLAGS_COMPILE = lib.optionalString stdenv.cc.isClang (toString [
     "-Wno-old-style-cast"
     "-Wno-error"
     "-D__BIG_ENDIAN__=${if stdenv.isBigEndian then "1" else "0"}"
-  ];
+  ]);
 
   NIX_LDFLAGS = lib.optionalString stdenv.isDarwin "-rpath ${libargon2}/lib";
 
diff --git a/pkgs/development/interpreters/kerf/default.nix b/pkgs/development/interpreters/kerf/default.nix
index e4fbc2bc6558..0987205f59d9 100644
--- a/pkgs/development/interpreters/kerf/default.nix
+++ b/pkgs/development/interpreters/kerf/default.nix
@@ -30,13 +30,13 @@ stdenv.mkDerivation rec {
   makeFlags = [ "kerf" "kerf_test" ];
 
   # avoid a huge amount of warnings to make failures clearer
-  env.NIX_CFLAGS_COMPILE = map (x: "-Wno-${x}") [
+  env.NIX_CFLAGS_COMPILE = toString (map (x: "-Wno-${x}") [
     "void-pointer-to-int-cast"
     "format"
     "implicit-function-declaration"
     "gnu-variable-sized-type-not-at-end"
     "unused-result"
-  ] ++ lib.optionals stdenv.isDarwin [ "-fcommon" ];
+  ] ++ lib.optionals stdenv.isDarwin [ "-fcommon" ]);
 
   patchPhase = ''
     substituteInPlace ./Makefile \
diff --git a/pkgs/development/libraries/liblastfm/default.nix b/pkgs/development/libraries/liblastfm/default.nix
index cfd56b5091ee..7dcc3b0d0cc0 100644
--- a/pkgs/development/libraries/liblastfm/default.nix
+++ b/pkgs/development/libraries/liblastfm/default.nix
@@ -23,10 +23,7 @@ stdenv.mkDerivation rec {
   buildInputs = [ fftwSinglePrec libsamplerate qtbase ]
     ++ lib.optional stdenv.isDarwin darwin.apple_sdk.frameworks.SystemConfiguration;
 
-  env.NIX_CFLAGS_COMPILE =
-    lib.optionals (stdenv.cc.isGNU && lib.versionAtLeast stdenv.cc.version "11") [
-      "-std=c++11"
-    ];
+  env.NIX_CFLAGS_COMPILE = lib.optionalString (stdenv.cc.isGNU && lib.versionAtLeast stdenv.cc.version "11") "-std=c++11";
 
   dontWrapQtApps = true;
 
diff --git a/pkgs/development/ocaml-modules/lablgtk/default.nix b/pkgs/development/ocaml-modules/lablgtk/default.nix
index 6b35bb423e3b..17e64cafb077 100644
--- a/pkgs/development/ocaml-modules/lablgtk/default.nix
+++ b/pkgs/development/ocaml-modules/lablgtk/default.nix
@@ -12,7 +12,7 @@ let param =
       rev = version;
       sha256 = "sha256-69Svno0qLaUifMscnVuPUJlCo9d8Lee+1qiYx34G3Po=";
     };
-    env.NIX_CFLAGS_COMPILE = null;
+    env = { };
     buildInputs = [ camlp-streams ];
   } else if check "3.12" then {
     version = "2.18.5";
diff --git a/pkgs/development/python-modules/py3exiv2/default.nix b/pkgs/development/python-modules/py3exiv2/default.nix
index a1951b5e1e71..de8cc23c8fb8 100644
--- a/pkgs/development/python-modules/py3exiv2/default.nix
+++ b/pkgs/development/python-modules/py3exiv2/default.nix
@@ -26,9 +26,7 @@ buildPythonPackage rec {
   ];
 
   # Work around Python distutils compiling C++ with $CC (see issue #26709)
-  env.NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin [
-    "-I${lib.getDev libcxx}/include/c++/v1"
-  ];
+  env.NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin "-I${lib.getDev libcxx}/include/c++/v1";
 
   pythonImportsCheck = [
     "pyexiv2"