diff --git a/pkgs/development/compilers/openjdk/8.nix b/pkgs/development/compilers/openjdk/8.nix
index 4debf10c0cb4..c6b3644fecca 100644
--- a/pkgs/development/compilers/openjdk/8.nix
+++ b/pkgs/development/compilers/openjdk/8.nix
@@ -140,7 +140,7 @@ let
 
     separateDebugInfo = true;
 
-    NIX_CFLAGS_COMPILE = [
+    NIX_CFLAGS_COMPILE = toString ([
       # glibc 2.24 deprecated readdir_r so we need this
       # See https://www.mail-archive.com/openembedded-devel@lists.openembedded.org/msg49006.html
       "-Wno-error=deprecated-declarations"
@@ -151,13 +151,13 @@ let
       "-fno-delete-null-pointer-checks"
       "-std=gnu++98"
       "-Wno-error"
-    ];
+    ]);
 
-    NIX_LDFLAGS= lib.optionals (!headless) [
+    NIX_LDFLAGS= toString (lib.optionals (!headless) [
       "-lfontconfig" "-lcups" "-lXinerama" "-lXrandr" "-lmagic"
     ] ++ lib.optionals (!headless && enableGnome2) [
       "-lgtk-x11-2.0" "-lgio-2.0" "-lgnomevfs-2" "-lgconf-2"
-    ];
+    ]);
 
     buildFlags = [ "all" ];
 
diff --git a/pkgs/development/compilers/rust/rustc.nix b/pkgs/development/compilers/rust/rustc.nix
index 49eaeef0d9c0..44bbd05aec73 100644
--- a/pkgs/development/compilers/rust/rustc.nix
+++ b/pkgs/development/compilers/rust/rustc.nix
@@ -41,11 +41,11 @@ in stdenv.mkDerivation rec {
   # See: https://github.com/NixOS/nixpkgs/pull/56540#issuecomment-471624656
   stripDebugList = [ "bin" ];
 
-  NIX_LDFLAGS =
+  NIX_LDFLAGS = toString (
        # when linking stage1 libstd: cc: undefined reference to `__cxa_begin_catch'
        optional (stdenv.isLinux && !withBundledLLVM) "--push-state --as-needed -lstdc++ --pop-state"
     ++ optional (stdenv.isDarwin && !withBundledLLVM) "-lc++"
-    ++ optional stdenv.isDarwin "-rpath ${llvmSharedForHost}/lib";
+    ++ optional stdenv.isDarwin "-rpath ${llvmSharedForHost}/lib");
 
   # Increase codegen units to introduce parallelism within the compiler.
   RUSTFLAGS = "-Ccodegen-units=10";
diff --git a/pkgs/development/interpreters/love/0.10.nix b/pkgs/development/interpreters/love/0.10.nix
index 6a3aa9f648f4..e1ca3ded2083 100644
--- a/pkgs/development/interpreters/love/0.10.nix
+++ b/pkgs/development/interpreters/love/0.10.nix
@@ -29,7 +29,7 @@ stdenv.mkDerivation {
     "--with-lua=luajit"
   ];
 
-  NIX_CFLAGS_COMPILE = [ "-DluaL_reg=luaL_Reg" ]; # needed since luajit-2.1.0-beta3
+  NIX_CFLAGS_COMPILE = "-DluaL_reg=luaL_Reg"; # needed since luajit-2.1.0-beta3
 
   meta = {
     homepage = http://love2d.org;
diff --git a/pkgs/development/libraries/gtk/3.x.nix b/pkgs/development/libraries/gtk/3.x.nix
index 7f09b52d51ff..5a2d9159cac2 100644
--- a/pkgs/development/libraries/gtk/3.x.nix
+++ b/pkgs/development/libraries/gtk/3.x.nix
@@ -88,10 +88,7 @@ stdenv.mkDerivation rec {
 
   # These are the defines that'd you'd get with --enable-debug=minimum (default).
   # See: https://developer.gnome.org/gtk3/stable/gtk-building.html#extra-configuration-options
-  NIX_CFLAGS_COMPILE = [
-    "-DG_ENABLE_DEBUG"
-    "-DG_DISABLE_CAST_CHECKS"
-  ];
+  NIX_CFLAGS_COMPILE = "-DG_ENABLE_DEBUG -DG_DISABLE_CAST_CHECKS";
 
   postPatch = ''
     files=(
diff --git a/pkgs/development/libraries/ilmbase/default.nix b/pkgs/development/libraries/ilmbase/default.nix
index a25a590b3705..00cdda1e5708 100644
--- a/pkgs/development/libraries/ilmbase/default.nix
+++ b/pkgs/development/libraries/ilmbase/default.nix
@@ -20,7 +20,7 @@ stdenv.mkDerivation rec {
   depsBuildBuild = [ buildPackages.stdenv.cc ];
   nativeBuildInputs = [ automake autoconf libtool which ];
 
-  NIX_CFLAGS_LINK = [ "-pthread" ];
+  NIX_CFLAGS_LINK = "-pthread";
 
   patches = [
     ./bootstrap.patch
diff --git a/pkgs/development/libraries/libcaca/default.nix b/pkgs/development/libraries/libcaca/default.nix
index 8949ea8e390e..7773fe46c0ce 100644
--- a/pkgs/development/libraries/libcaca/default.nix
+++ b/pkgs/development/libraries/libcaca/default.nix
@@ -19,12 +19,12 @@ stdenv.mkDerivation rec {
     (if x11Support then "--enable-x11" else "--disable-x11")
     ];
 
-  NIX_CFLAGS_COMPILE = stdenv.lib.optional (!x11Support) "-DX_DISPLAY_MISSING";
+  NIX_CFLAGS_COMPILE = stdenv.lib.optionalString (!x11Support) "-DX_DISPLAY_MISSING";
 
   enableParallelBuilding = true;
 
   propagatedBuildInputs = [ ncurses zlib pkgconfig (imlib2.override { inherit x11Support; }) ]
-    ++ stdenv.lib.optionals x11Support [ libX11 libXext];
+    ++ stdenv.lib.optionals x11Support [ libX11 libXext ];
 
   postInstall = ''
     mkdir -p $dev/bin
diff --git a/pkgs/development/libraries/smpeg/default.nix b/pkgs/development/libraries/smpeg/default.nix
index a7ffc146f414..4d74ee7ca063 100644
--- a/pkgs/development/libraries/smpeg/default.nix
+++ b/pkgs/development/libraries/smpeg/default.nix
@@ -40,7 +40,7 @@ stdenv.mkDerivation rec {
       --prefix PKG_CONFIG_PATH ":" "${SDL.dev}/lib/pkgconfig"
   '';
 
-  NIX_LDFLAGS = [ "-lX11" ];
+  NIX_LDFLAGS = "-lX11";
 
   meta = {
     homepage = http://icculus.org/smpeg/;
diff --git a/pkgs/development/python-modules/cffi/default.nix b/pkgs/development/python-modules/cffi/default.nix
index 15d15c23a8d2..b05aeebf9d4d 100644
--- a/pkgs/development/python-modules/cffi/default.nix
+++ b/pkgs/development/python-modules/cffi/default.nix
@@ -29,7 +29,8 @@ if isPyPy then null else buildPythonPackage rec {
   '';
 
   # The tests use -Werror but with python3.6 clang detects some unreachable code.
-  NIX_CFLAGS_COMPILE = stdenv.lib.optionals stdenv.cc.isClang [ "-Wno-unused-command-line-argument" "-Wno-unreachable-code" ];
+  NIX_CFLAGS_COMPILE = stdenv.lib.optionalString stdenv.cc.isClang
+    "-Wno-unused-command-line-argument -Wno-unreachable-code";
 
   doCheck = !stdenv.hostPlatform.isMusl && !stdenv.isDarwin; # TODO: Investigate
   checkPhase = ''
diff --git a/pkgs/development/tools/documentation/doxygen/default.nix b/pkgs/development/tools/documentation/doxygen/default.nix
index 0e20d690fd72..af73ce25d422 100644
--- a/pkgs/development/tools/documentation/doxygen/default.nix
+++ b/pkgs/development/tools/documentation/doxygen/default.nix
@@ -29,7 +29,7 @@ stdenv.mkDerivation rec {
     stdenv.lib.optional (qt4 != null) "-Dbuild_wizard=YES";
 
   NIX_CFLAGS_COMPILE =
-    stdenv.lib.optional stdenv.isDarwin "-mmacosx-version-min=10.9";
+    stdenv.lib.optionalString stdenv.isDarwin "-mmacosx-version-min=10.9";
 
   enableParallelBuilding = true;
   doCheck = false; # fails
diff --git a/pkgs/tools/misc/timidity/default.nix b/pkgs/tools/misc/timidity/default.nix
index 318ad6e3a9dc..c307c96199f2 100644
--- a/pkgs/tools/misc/timidity/default.nix
+++ b/pkgs/tools/misc/timidity/default.nix
@@ -13,7 +13,7 @@ stdenv.mkDerivation {
 
   configureFlags = [ "--enable-audio=oss,alsa,jack" "--enable-alsaseq" "--with-default-output=alsa" "--enable-ncurses" ];
 
-  NIX_LDFLAGS = ["-ljack -L${libjack2}/lib"];
+  NIX_LDFLAGS = "-ljack -L${libjack2}/lib";
 
   instruments = fetchurl {
     url = http://www.csee.umbc.edu/pub/midia/instruments.tar.gz;
diff --git a/pkgs/tools/networking/dhcp/default.nix b/pkgs/tools/networking/dhcp/default.nix
index f6c204d26b7d..5e552da98dfe 100644
--- a/pkgs/tools/networking/dhcp/default.nix
+++ b/pkgs/tools/networking/dhcp/default.nix
@@ -39,7 +39,7 @@ stdenv.mkDerivation rec {
     (lib.optional stdenv.isLinux "--with-randomdev=/dev/random")
   ] ++ stdenv.lib.optionals (openldap != null) [ "--with-ldap" "--with-ldapcrypto" ];
 
-  NIX_CFLAGS_COMPILE = [
+  NIX_CFLAGS_COMPILE = builtins.toString [
     "-Wno-error=pointer-compare"
     "-Wno-error=format-truncation"
     "-Wno-error=stringop-truncation"