diff --git a/pkgs/applications/audio/audacity/default.nix b/pkgs/applications/audio/audacity/default.nix
index 2fd3e5c27fe7..57e0c52e6406 100644
--- a/pkgs/applications/audio/audacity/default.nix
+++ b/pkgs/applications/audio/audacity/default.nix
@@ -28,7 +28,7 @@ stdenv.mkDerivation rec {
   ];
 
   # audacity only looks for lame and ffmpeg at runtime, so we need to link them in manually
-  NIX_LDFLAGS = [
+  NIX_LDFLAGS = toString [
     # LAME
     "-lmp3lame"
     # ffmpeg
diff --git a/pkgs/applications/graphics/ahoviewer/default.nix b/pkgs/applications/graphics/ahoviewer/default.nix
index fb06266cdc59..87bddf9099ee 100644
--- a/pkgs/applications/graphics/ahoviewer/default.nix
+++ b/pkgs/applications/graphics/ahoviewer/default.nix
@@ -29,9 +29,7 @@ stdenv.mkDerivation rec {
     gst_all_1.gst-plugins-base
   ] ++ stdenv.lib.optional useUnrar unrar;
 
-  NIX_LDFLAGS = [
-    "-lpthread"
-  ];
+  NIX_LDFLAGS = "-lpthread";
 
   postPatch = ''patchShebangs version.sh'';
 
diff --git a/pkgs/applications/graphics/gimp/plugins/default.nix b/pkgs/applications/graphics/gimp/plugins/default.nix
index fa29c979b050..0a06c42b5fc0 100644
--- a/pkgs/applications/graphics/gimp/plugins/default.nix
+++ b/pkgs/applications/graphics/gimp/plugins/default.nix
@@ -48,7 +48,7 @@ stdenv.lib.makeScope pkgs.newScope (self: with self; {
       url = https://ftp.gimp.org/pub/gimp/plug-ins/v2.6/gap/gimp-gap-2.6.0.tar.bz2;
       sha256 = "1jic7ixcmsn4kx2cn32nc5087rk6g8xsrz022xy11yfmgvhzb0ql";
     };
-    NIX_LDFLAGS = [ "-lm" ];
+    NIX_LDFLAGS = "-lm";
     patchPhase = ''
       sed -e 's,^\(GIMP_PLUGIN_DIR=\).*,\1'"$out/${gimp.name}-plugins", \
        -e 's,^\(GIMP_DATA_DIR=\).*,\1'"$out/share/${gimp.name}", -i configure
@@ -141,7 +141,7 @@ stdenv.lib.makeScope pkgs.newScope (self: with self; {
       Filters/Enhance/Wavelet sharpen
     */
     name = "wavelet-sharpen-0.1.2";
-    NIX_LDFLAGS = [ "-lm" ];
+    NIX_LDFLAGS = "-lm";
     src = fetchurl {
       url = http://registry.gimp.org/files/wavelet-sharpen-0.1.2.tar.gz;
       sha256 = "0vql1k67i21g5ivaa1jh56rg427m0icrkpryrhg75nscpirfxxqw";
diff --git a/pkgs/applications/networking/browsers/firefox/common.nix b/pkgs/applications/networking/browsers/firefox/common.nix
index d9dc0a4f7887..7b73027f203d 100644
--- a/pkgs/applications/networking/browsers/firefox/common.nix
+++ b/pkgs/applications/networking/browsers/firefox/common.nix
@@ -156,7 +156,7 @@ stdenv.mkDerivation rec {
                                      AVFoundation MediaToolbox CoreLocation
                                      Foundation libobjc AddressBook cups ];
 
-  NIX_CFLAGS_COMPILE = [
+  NIX_CFLAGS_COMPILE = toString ([
     "-I${glib.dev}/include/gio-unix-2.0"
   ]
   ++ lib.optionals (!isTorBrowserLike) [
@@ -164,7 +164,7 @@ stdenv.mkDerivation rec {
   ]
   ++ lib.optional (pname == "firefox-esr" && lib.versionAtLeast ffversion "68"
                                           && lib.versionOlder ffversion "69")
-    "-Wno-error=format-security";
+    "-Wno-error=format-security");
 
   postPatch = lib.optionalString (lib.versionAtLeast ffversion "63.0" && !isTorBrowserLike) ''
     substituteInPlace third_party/prio/prio/rand.c --replace 'nspr/prinit.h' 'prinit.h'
diff --git a/pkgs/applications/science/logic/avy/default.nix b/pkgs/applications/science/logic/avy/default.nix
index 9b59828ddab7..b43e0c6fbf1a 100644
--- a/pkgs/applications/science/logic/avy/default.nix
+++ b/pkgs/applications/science/logic/avy/default.nix
@@ -12,14 +12,14 @@ stdenv.mkDerivation {
   };
 
   buildInputs = [ cmake zlib boost.out boost.dev ];
-  NIX_CFLAGS_COMPILE = [ "-Wno-narrowing" ]
+  NIX_CFLAGS_COMPILE = toString ([ "-Wno-narrowing" ]
     # Squelch endless stream of warnings on same few things
     ++ stdenv.lib.optionals stdenv.cc.isClang [
       "-Wno-empty-body"
       "-Wno-tautological-compare"
       "-Wc++11-compat-deprecated-writable-strings"
       "-Wno-deprecated"
-    ];
+    ]);
 
   prePatch = ''
     sed -i -e '1i#include <stdint.h>' abc/src/bdd/dsd/dsd.h
diff --git a/pkgs/applications/video/aegisub/default.nix b/pkgs/applications/video/aegisub/default.nix
index 83f7ebc29d19..123308babeae 100644
--- a/pkgs/applications/video/aegisub/default.nix
+++ b/pkgs/applications/video/aegisub/default.nix
@@ -108,9 +108,7 @@ stdenv.mkDerivation
 
   # this is fixed upstream though not yet in an officially released version,
   # should be fine remove on next release (if one ever happens)
-  NIX_LDFLAGS = [
-    "-lpthread"
-  ];
+  NIX_LDFLAGS = "-lpthread";
 
   postInstall = "ln -s $out/bin/aegisub-* $out/bin/aegisub";
 
diff --git a/pkgs/applications/video/mplayer/default.nix b/pkgs/applications/video/mplayer/default.nix
index a75a7a11d67a..f5559e3fb6c0 100644
--- a/pkgs/applications/video/mplayer/default.nix
+++ b/pkgs/applications/video/mplayer/default.nix
@@ -195,11 +195,11 @@ stdenv.mkDerivation rec {
     echo CONFIG_MPEGAUDIODSP=yes >> config.mak
   '';
 
-  NIX_LDFLAGS = with stdenv.lib;
+  NIX_LDFLAGS = with stdenv.lib; toString (
        optional  fontconfigSupport "-lfontconfig"
     ++ optional  fribidiSupport "-lfribidi"
     ++ optionals x11Support [ "-lX11" "-lXext" ]
-    ;
+  );
 
   installTargets = [ "install" ] ++ stdenv.lib.optional x11Support "install-gui";
 
diff --git a/pkgs/desktops/gnome-3/core/gnome-settings-daemon/default.nix b/pkgs/desktops/gnome-3/core/gnome-settings-daemon/default.nix
index 36da3349c46a..c388c4f7211b 100644
--- a/pkgs/desktops/gnome-3/core/gnome-settings-daemon/default.nix
+++ b/pkgs/desktops/gnome-3/core/gnome-settings-daemon/default.nix
@@ -99,11 +99,9 @@ stdenv.mkDerivation rec {
     "-Dudev_dir=${placeholder "out"}/lib/udev"
   ];
 
-  NIX_CFLAGS_COMPILE = [
-    # Default for release buildtype but passed manually because
-    # we're using plain
-    "-DG_DISABLE_CAST_CHECKS"
-  ];
+  # Default for release buildtype but passed manually because
+  # we're using plain
+  NIX_CFLAGS_COMPILE = "-DG_DISABLE_CAST_CHECKS";
 
   # So the polkit policy can reference /run/current-system/sw/bin/gnome-settings-daemon/gsd-backlight-helper
   postFixup = ''
diff --git a/pkgs/development/libraries/argp-standalone/default.nix b/pkgs/development/libraries/argp-standalone/default.nix
index 8fe3bd287c10..6544c4811875 100644
--- a/pkgs/development/libraries/argp-standalone/default.nix
+++ b/pkgs/development/libraries/argp-standalone/default.nix
@@ -31,7 +31,7 @@ stdenv.mkDerivation {
        stdenv.lib.optionals stdenv.hostPlatform.isDarwin [ patch-argp-fmtstream ]
     ++ stdenv.lib.optionals stdenv.hostPlatform.isLinux [ patch-throw-in-funcdef patch-shared ];
 
-  patchFlags = stdenv.lib.optionalString stdenv.hostPlatform.isDarwin "-p0";
+  patchFlags = stdenv.lib.optional stdenv.hostPlatform.isDarwin "-p0";
 
   preConfigure = stdenv.lib.optionalString stdenv.hostPlatform.isLinux "export CFLAGS='-fgnu89-inline'";
 
diff --git a/pkgs/development/libraries/aws-c-common/default.nix b/pkgs/development/libraries/aws-c-common/default.nix
index 4286eedc87b2..b10797d3d56f 100644
--- a/pkgs/development/libraries/aws-c-common/default.nix
+++ b/pkgs/development/libraries/aws-c-common/default.nix
@@ -13,10 +13,8 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ cmake ];
 
-  NIX_CFLAGS_COMPILE = lib.optionals stdenv.isDarwin [
-    "-Wno-nullability-extension"
-    "-Wno-typedef-redefinition"
-  ];
+  NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin
+    "-Wno-nullability-extension -Wno-typedef-redefinition";
 
   meta = with lib; {
     description = "AWS SDK for C common core";
diff --git a/pkgs/development/libraries/glm/default.nix b/pkgs/development/libraries/glm/default.nix
index 88b33601ee70..d39d6f0d7a36 100644
--- a/pkgs/development/libraries/glm/default.nix
+++ b/pkgs/development/libraries/glm/default.nix
@@ -27,9 +27,7 @@ stdenv.mkDerivation rec {
     cp ${gcc7PlatformPatch} glm/simd/platform.h
   '';
 
-  NIX_CFLAGS_COMPILE = stdenv.lib.optionals stdenv.isDarwin [
-    "-DGLM_COMPILER=0"
-  ];
+  NIX_CFLAGS_COMPILE = stdenv.lib.optionalString stdenv.isDarwin "-DGLM_COMPILER=0";
 
   postInstall = ''
     mkdir -p $doc/share/doc/glm
diff --git a/pkgs/development/libraries/gpgme/default.nix b/pkgs/development/libraries/gpgme/default.nix
index 63072273c2ed..ed2b5563bd37 100644
--- a/pkgs/development/libraries/gpgme/default.nix
+++ b/pkgs/development/libraries/gpgme/default.nix
@@ -47,12 +47,12 @@ stdenv.mkDerivation rec {
   # fit in the limit. https://github.com/NixOS/nix/pull/1085
     ++ lib.optionals stdenv.isDarwin [ "--disable-gpg-test" ];
 
-  NIX_CFLAGS_COMPILE =
+  NIX_CFLAGS_COMPILE = toString (
     # qgpgme uses Q_ASSERT which retains build inputs at runtime unless
     # debugging is disabled
     lib.optional (qtbase != null) "-DQT_NO_DEBUG"
     # https://www.gnupg.org/documentation/manuals/gpgme/Largefile-Support-_0028LFS_0029.html
-    ++ lib.optional (system == "i686-linux") "-D_FILE_OFFSET_BITS=64";
+    ++ lib.optional (system == "i686-linux") "-D_FILE_OFFSET_BITS=64");
 
   checkInputs = [ which ];
 
diff --git a/pkgs/development/libraries/gsl/default.nix b/pkgs/development/libraries/gsl/default.nix
index 1fd086ca23c7..966d6a8ffd5d 100644
--- a/pkgs/development/libraries/gsl/default.nix
+++ b/pkgs/development/libraries/gsl/default.nix
@@ -9,7 +9,7 @@ stdenv.mkDerivation rec {
   };
 
   # do not let -march=skylake to enable FMA (https://lists.gnu.org/archive/html/bug-gsl/2011-11/msg00019.html)
-  NIX_CFLAGS_COMPILE = stdenv.lib.optional stdenv.isx86_64 "-mno-fma";
+  NIX_CFLAGS_COMPILE = stdenv.lib.optionalString stdenv.isx86_64 "-mno-fma";
 
   # https://lists.gnu.org/archive/html/bug-gsl/2015-11/msg00012.html
   doCheck = stdenv.hostPlatform.system != "i686-linux" && stdenv.hostPlatform.system != "aarch64-linux";
diff --git a/pkgs/development/libraries/gsl/gsl-1_16.nix b/pkgs/development/libraries/gsl/gsl-1_16.nix
index e5772c8772ec..ae102ac60307 100644
--- a/pkgs/development/libraries/gsl/gsl-1_16.nix
+++ b/pkgs/development/libraries/gsl/gsl-1_16.nix
@@ -9,7 +9,7 @@ stdenv.mkDerivation rec {
   };
 
   # do not let -march=skylake to enable FMA (https://lists.gnu.org/archive/html/bug-gsl/2011-11/msg00019.html)
-  NIX_CFLAGS_COMPILE = stdenv.lib.optional stdenv.isx86_64 "-mno-fma";
+  NIX_CFLAGS_COMPILE = stdenv.lib.optionalString stdenv.isx86_64 "-mno-fma";
 
   patches = [
     (fetchpatch {
diff --git a/pkgs/development/libraries/libbluray/default.nix b/pkgs/development/libraries/libbluray/default.nix
index 517251e137ef..daa349ca6309 100644
--- a/pkgs/development/libraries/libbluray/default.nix
+++ b/pkgs/development/libraries/libbluray/default.nix
@@ -40,7 +40,7 @@ stdenv.mkDerivation rec {
 
   propagatedBuildInputs = optional withAACS libaacs;
 
-  NIX_LDFLAGS = [
+  NIX_LDFLAGS = toString [
     (optionalString withAACS   "-L${libaacs}/lib -laacs")
     (optionalString withBDplus "-L${libbdplus}/lib -lbdplus")
   ];
diff --git a/pkgs/development/libraries/libunique/default.nix b/pkgs/development/libraries/libunique/default.nix
index e0022411221d..d6566978a6bb 100644
--- a/pkgs/development/libraries/libunique/default.nix
+++ b/pkgs/development/libraries/libunique/default.nix
@@ -10,7 +10,7 @@ stdenv.mkDerivation rec {
   };
 
   # glib-2.62 deprecations
-  NIX_CFLAGS_COMPILE = [ "-DGLIB_DISABLE_DEPRECATION_WARNINGS" ];
+  NIX_CFLAGS_COMPILE = "-DGLIB_DISABLE_DEPRECATION_WARNINGS";
 
   # Patches from Gentoo portage
   patches = [
diff --git a/pkgs/development/libraries/opencv/3.x.nix b/pkgs/development/libraries/opencv/3.x.nix
index 97df84637ef7..642facf166a6 100644
--- a/pkgs/development/libraries/opencv/3.x.nix
+++ b/pkgs/development/libraries/opencv/3.x.nix
@@ -208,7 +208,7 @@ stdenv.mkDerivation {
 
   nativeBuildInputs = [ cmake pkgconfig unzip ];
 
-  NIX_CFLAGS_COMPILE = lib.optional enableEXR "-I${ilmbase.dev}/include/OpenEXR";
+  NIX_CFLAGS_COMPILE = lib.optionalString enableEXR "-I${ilmbase.dev}/include/OpenEXR";
 
   # Configure can't find the library without this.
   OpenBLAS_HOME = lib.optionalString enableOpenblas openblas;
diff --git a/pkgs/development/libraries/qt-4.x/4.8/default.nix b/pkgs/development/libraries/qt-4.x/4.8/default.nix
index 632b5fc1fd5e..25953949eb76 100644
--- a/pkgs/development/libraries/qt-4.x/4.8/default.nix
+++ b/pkgs/development/libraries/qt-4.x/4.8/default.nix
@@ -206,13 +206,13 @@ stdenv.mkDerivation rec {
 
   enableParallelBuilding = true;
 
-  NIX_CFLAGS_COMPILE =
+  NIX_CFLAGS_COMPILE = toString (
     # with gcc7 the warnings blow the log over Hydra's limit
     [ "-Wno-expansion-to-defined" "-Wno-unused-local-typedefs" ]
     ++ lib.optional stdenv.isLinux "-std=gnu++98" # gnu++ in (Obj)C flags is no good on Darwin
     ++ lib.optionals (stdenv.isFreeBSD || stdenv.isDarwin)
       [ "-I${glib.dev}/include/glib-2.0" "-I${glib.out}/lib/glib-2.0/include" ]
-    ++ lib.optional stdenv.isDarwin "-I${libcxx}/include/c++/v1";
+    ++ lib.optional stdenv.isDarwin "-I${libcxx}/include/c++/v1");
 
   NIX_LDFLAGS = lib.optionalString (stdenv.isFreeBSD || stdenv.isDarwin) "-lglib-2.0";
 
diff --git a/pkgs/development/libraries/qt-5/mkDerivation.nix b/pkgs/development/libraries/qt-5/mkDerivation.nix
index 95357c096dfd..2c6333cb0204 100644
--- a/pkgs/development/libraries/qt-5/mkDerivation.nix
+++ b/pkgs/development/libraries/qt-5/mkDerivation.nix
@@ -12,9 +12,9 @@ let
     qmakeFlags = [ ("CONFIG+=" + (if debug then "debug" else "release")) ]
               ++ (args.qmakeFlags or []);
 
-    NIX_CFLAGS_COMPILE =
+    NIX_CFLAGS_COMPILE = toString (
       optional (!debug) "-DQT_NO_DEBUG"
-      ++ lib.toList (args.NIX_CFLAGS_COMPILE or []);
+      ++ lib.toList (args.NIX_CFLAGS_COMPILE or []));
 
     cmakeFlags =
       (args.cmakeFlags or [])
diff --git a/pkgs/development/libraries/qt-5/modules/qtbase.nix b/pkgs/development/libraries/qt-5/modules/qtbase.nix
index c7cb6d509dc2..cd426884d12d 100644
--- a/pkgs/development/libraries/qt-5/modules/qtbase.nix
+++ b/pkgs/development/libraries/qt-5/modules/qtbase.nix
@@ -200,20 +200,17 @@ stdenv.mkDerivation {
     done
   '';
 
-  NIX_CFLAGS_COMPILE =
-    [
-      "-Wno-error=sign-compare" # freetype-2.5.4 changed signedness of some struct fields
-      ''-DNIXPKGS_QTCOMPOSE="${libX11.out}/share/X11/locale"''
-      ''-D${if compareVersion "5.11.0" >= 0 then "LIBRESOLV_SO" else "NIXPKGS_LIBRESOLV"}="${stdenv.cc.libc.out}/lib/libresolv"''
-      ''-DNIXPKGS_LIBXCURSOR="${libXcursor.out}/lib/libXcursor"''
-    ]
-
-    ++ lib.optional libGLSupported ''-DNIXPKGS_MESA_GL="${libGL.out}/lib/libGL"''
+  NIX_CFLAGS_COMPILE = toString ([
+    "-Wno-error=sign-compare" # freetype-2.5.4 changed signedness of some struct fields
+    ''-DNIXPKGS_QTCOMPOSE="${libX11.out}/share/X11/locale"''
+    ''-D${if compareVersion "5.11.0" >= 0 then "LIBRESOLV_SO" else "NIXPKGS_LIBRESOLV"}="${stdenv.cc.libc.out}/lib/libresolv"''
+    ''-DNIXPKGS_LIBXCURSOR="${libXcursor.out}/lib/libXcursor"''
+  ] ++ lib.optional libGLSupported ''-DNIXPKGS_MESA_GL="${libGL.out}/lib/libGL"''
     ++ lib.optionals withGtk3 [
          ''-DNIXPKGS_QGTK3_XDG_DATA_DIRS="${gtk3}/share/gsettings-schemas/${gtk3.name}"''
          ''-DNIXPKGS_QGTK3_GIO_EXTRA_MODULES="${dconf.lib}/lib/gio/modules"''
        ]
-    ++ lib.optional decryptSslTraffic "-DQT_DECRYPT_SSL_TRAFFIC";
+    ++ lib.optional decryptSslTraffic "-DQT_DECRYPT_SSL_TRAFFIC");
 
   prefixKey = "-prefix ";
 
diff --git a/pkgs/development/libraries/tinyxml/2.6.2.nix b/pkgs/development/libraries/tinyxml/2.6.2.nix
index cc7c996f7c3a..0cc4038b64e7 100644
--- a/pkgs/development/libraries/tinyxml/2.6.2.nix
+++ b/pkgs/development/libraries/tinyxml/2.6.2.nix
@@ -28,7 +28,7 @@ in stdenv.mkDerivation {
   hardeningDisable = [ "format" ];
 
   NIX_CFLAGS_COMPILE =
-    stdenv.lib.optional stdenv.isDarwin "-mmacosx-version-min=10.9";
+    stdenv.lib.optionalString stdenv.isDarwin "-mmacosx-version-min=10.9";
 
   buildInputs = [ unzip ];
   buildPhase = ''
diff --git a/pkgs/development/libraries/usbredir/default.nix b/pkgs/development/libraries/usbredir/default.nix
index 2eee80a76969..8e43135196c9 100644
--- a/pkgs/development/libraries/usbredir/default.nix
+++ b/pkgs/development/libraries/usbredir/default.nix
@@ -9,7 +9,7 @@ stdenv.mkDerivation rec {
     sha256 = "002yik1x7kn0427xahvnhjby2np14a6xqw7c3dx530n9h5d9rg47";
   };
 
-  NIX_CFLAGS_COMPILE = [ "-Wno-error" ];
+  NIX_CFLAGS_COMPILE = "-Wno-error";
 
   nativeBuildInputs = [ pkgconfig ];
   buildInputs = [ libusb ];
diff --git a/pkgs/development/libraries/wxwidgets/2.8/default.nix b/pkgs/development/libraries/wxwidgets/2.8/default.nix
index 38ee4376ac2d..73dac47307a9 100644
--- a/pkgs/development/libraries/wxwidgets/2.8/default.nix
+++ b/pkgs/development/libraries/wxwidgets/2.8/default.nix
@@ -44,7 +44,7 @@ stdenv.mkDerivation rec {
     + optionalString withMesa "${libGLU.out}/lib ${libGL.out}/lib ";
 
   # Work around a bug in configure.
-  NIX_CFLAGS_COMPILE = [ "-DHAVE_X11_XLIB_H=1" "-lX11" "-lcairo" "-Wno-narrowing" ];
+  NIX_CFLAGS_COMPILE = "-DHAVE_X11_XLIB_H=1 -lX11 -lcairo -Wno-narrowing";
 
   preConfigure = "
     substituteInPlace configure --replace 'SEARCH_INCLUDE=' 'DUMMY_SEARCH_INCLUDE='
diff --git a/pkgs/games/airstrike/default.nix b/pkgs/games/airstrike/default.nix
index 19d2a01b4729..408f2817854a 100644
--- a/pkgs/games/airstrike/default.nix
+++ b/pkgs/games/airstrike/default.nix
@@ -11,9 +11,7 @@ stdenv.mkDerivation rec {
 
   buildInputs = [ makeWrapper SDL SDL_image ];
 
-  NIX_LDFLAGS = [
-    "-lm"
-  ];
+  NIX_LDFLAGS = "-lm";
 
   installPhase = ''
     ls -l
diff --git a/pkgs/games/armagetronad/default.nix b/pkgs/games/armagetronad/default.nix
index edb739125c01..57373d39b54c 100644
--- a/pkgs/games/armagetronad/default.nix
+++ b/pkgs/games/armagetronad/default.nix
@@ -14,7 +14,7 @@ stdenv.mkDerivation {
     sha256 = "157pp84wf0q3bdb72rnbm3ck0czwx2ply6lyhj8z7kfdc7csdbr3";
   };
 
-  NIX_LDFLAGS = [ "-lSDL_image" ];
+  NIX_LDFLAGS = "-lSDL_image";
 
   enableParallelBuilding = true;
 
diff --git a/pkgs/servers/mail/archiveopteryx/default.nix b/pkgs/servers/mail/archiveopteryx/default.nix
index 3443a508aea4..55cc4c121f0f 100644
--- a/pkgs/servers/mail/archiveopteryx/default.nix
+++ b/pkgs/servers/mail/archiveopteryx/default.nix
@@ -21,7 +21,7 @@ stdenv.mkDerivation rec {
   '';
 
   # fix build on gcc7+
-  NIX_CFLAGS_COMPILE = [
+  NIX_CFLAGS_COMPILE = builtins.toString [
     "-Wno-error=builtin-declaration-mismatch"
     "-Wno-error=implicit-fallthrough"
     "-Wno-error=deprecated-copy"
diff --git a/pkgs/servers/nosql/arangodb/default.nix b/pkgs/servers/nosql/arangodb/default.nix
index ef75dad91517..e41930a2f485 100644
--- a/pkgs/servers/nosql/arangodb/default.nix
+++ b/pkgs/servers/nosql/arangodb/default.nix
@@ -17,7 +17,7 @@ let
 
     # prevent failing with "cmake-3.13.4/nix-support/setup-hook: line 10: ./3rdParty/rocksdb/RocksDBConfig.cmake.in: No such file or directory"
     dontFixCmake       =                     lib.versionAtLeast version "3.5";
-    NIX_CFLAGS_COMPILE = lib.optionals      (lib.versionAtLeast version "3.5") [ "-Wno-error" ];
+    NIX_CFLAGS_COMPILE = lib.optionalString (lib.versionAtLeast version "3.5") "-Wno-error";
     preConfigure       = lib.optionalString (lib.versionAtLeast version "3.5") "patchShebangs utils";
 
     postPatch = ''
diff --git a/pkgs/servers/sql/postgresql/default.nix b/pkgs/servers/sql/postgresql/default.nix
index 440375db841d..3f05b3e36c19 100644
--- a/pkgs/servers/sql/postgresql/default.nix
+++ b/pkgs/servers/sql/postgresql/default.nix
@@ -44,7 +44,7 @@ let
 
     buildFlags = [ "world" ];
 
-    NIX_CFLAGS_COMPILE = [ "-I${libxml2.dev}/include/libxml2" ];
+    NIX_CFLAGS_COMPILE = "-I${libxml2.dev}/include/libxml2";
 
     # Otherwise it retains a reference to compiler and fails; see #44767.  TODO: better.
     preConfigure = "CC=${stdenv.cc.targetPrefix}cc";
diff --git a/pkgs/tools/graphics/appleseed/default.nix b/pkgs/tools/graphics/appleseed/default.nix
index d45c28528e72..cafe0bb7b11a 100644
--- a/pkgs/tools/graphics/appleseed/default.nix
+++ b/pkgs/tools/graphics/appleseed/default.nix
@@ -24,7 +24,7 @@ in stdenv.mkDerivation rec {
     osl seexpr makeWrapper
   ];
 
-  NIX_CFLAGS_COMPILE = [
+  NIX_CFLAGS_COMPILE = toString [
     "-I${openexr.dev}/include/OpenEXR"
     "-I${ilmbase.dev}/include/OpenEXR"
     "-I${openimageio.dev}/include/OpenImageIO"
diff --git a/pkgs/tools/graphics/asymptote/default.nix b/pkgs/tools/graphics/asymptote/default.nix
index 14b15686d720..31bdba26783e 100644
--- a/pkgs/tools/graphics/asymptote/default.nix
+++ b/pkgs/tools/graphics/asymptote/default.nix
@@ -54,7 +54,7 @@ stdenv.mkDerivation rec {
     "--with-context=$out/share/texmf/tex/context/third"
   ];
 
-  NIX_CFLAGS_COMPILE = [ "-I${boehmgc.dev}/include/gc" ];
+  NIX_CFLAGS_COMPILE = "-I${boehmgc.dev}/include/gc";
 
   postInstall = ''
     mv $out/share/info/asymptote/*.info $out/share/info/
diff --git a/pkgs/tools/graphics/zbar/default.nix b/pkgs/tools/graphics/zbar/default.nix
index 9a071e6150f9..7610b4e56fb0 100644
--- a/pkgs/tools/graphics/zbar/default.nix
+++ b/pkgs/tools/graphics/zbar/default.nix
@@ -53,7 +53,7 @@ stdenv.mkDerivation rec {
   ];
 
   # Disable assertions which include -dev QtBase file paths.
-  NIX_CFLAGS_COMPILE = [ "-DQT_NO_DEBUG" ];
+  NIX_CFLAGS_COMPILE = "-DQT_NO_DEBUG";
 
   configureFlags = [
     "--without-python"
diff --git a/pkgs/tools/networking/altermime/default.nix b/pkgs/tools/networking/altermime/default.nix
index e9091086ed98..b1481b2208c6 100644
--- a/pkgs/tools/networking/altermime/default.nix
+++ b/pkgs/tools/networking/altermime/default.nix
@@ -10,7 +10,8 @@ stdenv.mkDerivation rec {
     sha256 = "15zxg6spcmd35r6xbidq2fgcg2nzyv1sbbqds08lzll70mqx4pj7";
   };
 
-  NIX_CFLAGS_COMPILE = [ "-Wno-error=format"
+  NIX_CFLAGS_COMPILE = toString [
+    "-Wno-error=format"
     "-Wno-error=format-truncation"
     "-Wno-error=pointer-compare"
     "-Wno-error=memset-elt-size"
diff --git a/pkgs/tools/networking/atinout/default.nix b/pkgs/tools/networking/atinout/default.nix
index 175ba3960eef..16b3ee668da6 100644
--- a/pkgs/tools/networking/atinout/default.nix
+++ b/pkgs/tools/networking/atinout/default.nix
@@ -4,7 +4,7 @@ stdenv.mkDerivation rec {
   name = "atinout-${version}";
   version = "0.9.2-alpha";
 
-  NIX_CFLAGS_COMPILE = [ "-Werror=implicit-fallthrough=0" ];
+  NIX_CFLAGS_COMPILE = "-Werror=implicit-fallthrough=0";
   LANG = "C.UTF-8";
   nativeBuildInputs = [ ronn mount ];
 
diff --git a/pkgs/tools/video/mjpegtools/default.nix b/pkgs/tools/video/mjpegtools/default.nix
index 31d26a6c72a3..3e72d8b8af59 100644
--- a/pkgs/tools/video/mjpegtools/default.nix
+++ b/pkgs/tools/video/mjpegtools/default.nix
@@ -21,7 +21,7 @@ stdenv.mkDerivation rec {
   buildInputs = [ libdv libjpeg libpng ]
               ++ lib.optionals (!withMinimal) [ gtk2 libX11 SDL SDL_gfx ];
 
-  NIX_CFLAGS_COMPILE = lib.optional (!withMinimal) "-I${SDL.dev}/include/SDL";
+  NIX_CFLAGS_COMPILE = lib.optionalString (!withMinimal) "-I${SDL.dev}/include/SDL";
 
   postPatch = ''
     sed -i -e '/ARCHFLAGS=/s:=.*:=:' configure