diff --git a/pkgs/development/libraries/gdbm/default.nix b/pkgs/development/libraries/gdbm/default.nix
index 972e9022235a..830a311db706 100644
--- a/pkgs/development/libraries/gdbm/default.nix
+++ b/pkgs/development/libraries/gdbm/default.nix
@@ -4,9 +4,6 @@ stdenv.mkDerivation rec {
   pname = "gdbm";
   version = "1.18.1";
 
-  # FIXME: remove on update to > 1.18.1
-  NIX_CFLAGS_COMPILE = if stdenv.cc.isClang then "-Wno-error=return-type" else null;
-
   src = fetchurl {
     url = "mirror://gnu/gdbm/${pname}-${version}.tar.gz";
     sha256 = "1p4ibds6z3ccy65lkmd6lm7js0kwifvl53r0fd759fjxgr917rl6";
diff --git a/pkgs/development/libraries/glib/default.nix b/pkgs/development/libraries/glib/default.nix
index 67d3c35609e6..0febed9f9c96 100644
--- a/pkgs/development/libraries/glib/default.nix
+++ b/pkgs/development/libraries/glib/default.nix
@@ -118,7 +118,7 @@ stdenv.mkDerivation rec {
     "-Ddevbindir=${placeholder ''dev''}/bin"
   ];
 
-  NIX_CFLAGS_COMPILE = [
+  NIX_CFLAGS_COMPILE = toString [
     "-Wno-error=nonnull"
     # Default for release buildtype but passed manually because
     # we're using plain
diff --git a/pkgs/development/libraries/libglvnd/default.nix b/pkgs/development/libraries/libglvnd/default.nix
index c2a5cfbed744..55b801b0b0d5 100644
--- a/pkgs/development/libraries/libglvnd/default.nix
+++ b/pkgs/development/libraries/libglvnd/default.nix
@@ -39,13 +39,13 @@ stdenv.mkDerivation rec {
       --replace "-Xlinker --version-script=$(VERSION_SCRIPT)" "-Xlinker"
   '';
 
-  NIX_CFLAGS_COMPILE = [
+  NIX_CFLAGS_COMPILE = toString ([
     "-UDEFAULT_EGL_VENDOR_CONFIG_DIRS"
     # FHS paths are added so that non-NixOS applications can find vendor files.
     "-DDEFAULT_EGL_VENDOR_CONFIG_DIRS=\"${addOpenGLRunpath.driverLink}/share/glvnd/egl_vendor.d:/etc/glvnd/egl_vendor.d:/usr/share/glvnd/egl_vendor.d\""
 
     "-Wno-error=array-bounds"
-  ] ++ lib.optional stdenv.cc.isClang "-Wno-error";
+  ] ++ lib.optional stdenv.cc.isClang "-Wno-error");
 
   # Indirectly: https://bugs.freedesktop.org/show_bug.cgi?id=35268
   configureFlags  = stdenv.lib.optional stdenv.hostPlatform.isMusl "--disable-tls";
diff --git a/pkgs/development/libraries/libpfm/default.nix b/pkgs/development/libraries/libpfm/default.nix
index f48c605dafd6..3398d3feb94f 100644
--- a/pkgs/development/libraries/libpfm/default.nix
+++ b/pkgs/development/libraries/libpfm/default.nix
@@ -16,7 +16,7 @@ stdenv.mkDerivation (rec {
     "SYS=${stdenv.hostPlatform.uname.system}"
   ];
 
-  NIX_CFLAGS_COMPILE = [ "-Wno-error" ];
+  NIX_CFLAGS_COMPILE = "-Wno-error";
 
   meta = with stdenv.lib; {
     description = "Helper library to program the performance monitoring events";
diff --git a/pkgs/development/libraries/libvdpau/default.nix b/pkgs/development/libraries/libvdpau/default.nix
index 792a31bcf9f9..e6a57f1e38c4 100644
--- a/pkgs/development/libraries/libvdpau/default.nix
+++ b/pkgs/development/libraries/libvdpau/default.nix
@@ -19,7 +19,7 @@ stdenv.mkDerivation rec {
   configureFlags = stdenv.lib.optional stdenv.isLinux
     "--with-module-dir=${mesa.drivers.driverLink}/lib/vdpau";
 
-  NIX_LDFLAGS = if stdenv.isDarwin then "-lX11" else null;
+  NIX_LDFLAGS = stdenv.lib.optionalString stdenv.isDarwin "-lX11";
 
   installFlags = [ "moduledir=$(out)/lib/vdpau" ];
 
diff --git a/pkgs/development/libraries/openal-soft/default.nix b/pkgs/development/libraries/openal-soft/default.nix
index 76f2861428d6..20528ac9284f 100644
--- a/pkgs/development/libraries/openal-soft/default.nix
+++ b/pkgs/development/libraries/openal-soft/default.nix
@@ -35,9 +35,9 @@ stdenv.mkDerivation rec {
     ++ optional pulseSupport libpulseaudio
     ++ optionals stdenv.isDarwin [ CoreServices AudioUnit AudioToolbox ];
 
-  NIX_LDFLAGS = []
+  NIX_LDFLAGS = toString ([]
     ++ optional alsaSupport "-lasound"
-    ++ optional pulseSupport "-lpulse";
+    ++ optional pulseSupport "-lpulse");
 
   meta = {
     description = "OpenAL alternative";
diff --git a/pkgs/development/libraries/sqlite/default.nix b/pkgs/development/libraries/sqlite/default.nix
index 5837361e01bc..d904637fcd38 100644
--- a/pkgs/development/libraries/sqlite/default.nix
+++ b/pkgs/development/libraries/sqlite/default.nix
@@ -25,7 +25,7 @@ stdenv.mkDerivation rec {
 
   configureFlags = [ "--enable-threadsafe" ] ++ optional interactive "--enable-readline";
 
-  NIX_CFLAGS_COMPILE = [
+  NIX_CFLAGS_COMPILE = toString [
     "-DSQLITE_ENABLE_COLUMN_METADATA"
     "-DSQLITE_ENABLE_DBSTAT_VTAB"
     "-DSQLITE_ENABLE_JSON1"
diff --git a/pkgs/os-specific/linux/libselinux/default.nix b/pkgs/os-specific/linux/libselinux/default.nix
index d8a2298f3d3f..39e97f8473c8 100644
--- a/pkgs/os-specific/linux/libselinux/default.nix
+++ b/pkgs/os-specific/linux/libselinux/default.nix
@@ -26,7 +26,7 @@ stdenv.mkDerivation rec {
   # command-line>:0:0: error: "_FORTIFY_SOURCE" redefined [-Werror]
   hardeningDisable = [ "fortify" ];
 
-  NIX_CFLAGS_COMPILE = [ "-Wno-error" ];
+  NIX_CFLAGS_COMPILE = "-Wno-error";
 
   makeFlags = [
     "PREFIX=$(out)"
diff --git a/pkgs/os-specific/linux/libsepol/default.nix b/pkgs/os-specific/linux/libsepol/default.nix
index 03bd0252c5ca..b31554d6cee4 100644
--- a/pkgs/os-specific/linux/libsepol/default.nix
+++ b/pkgs/os-specific/linux/libsepol/default.nix
@@ -25,7 +25,7 @@ stdenv.mkDerivation rec {
     "SHLIBDIR=$(out)/lib"
   ];
 
-  NIX_CFLAGS_COMPILE = [ "-Wno-error" ];
+  NIX_CFLAGS_COMPILE = "-Wno-error";
 
   passthru = { inherit se_release se_url; };
 
diff --git a/pkgs/os-specific/linux/systemd/default.nix b/pkgs/os-specific/linux/systemd/default.nix
index 3cc976a909dd..3462801c07c4 100644
--- a/pkgs/os-specific/linux/systemd/default.nix
+++ b/pkgs/os-specific/linux/systemd/default.nix
@@ -180,18 +180,18 @@ in stdenv.mkDerivation {
       --replace "SYSTEMD_CGROUP_AGENT_PATH" "_SYSTEMD_CGROUP_AGENT_PATH"
   '';
 
-  NIX_CFLAGS_COMPILE =
-    [ # Can't say ${polkit.bin}/bin/pkttyagent here because that would
-      # lead to a cyclic dependency.
-      "-UPOLKIT_AGENT_BINARY_PATH" "-DPOLKIT_AGENT_BINARY_PATH=\"/run/current-system/sw/bin/pkttyagent\""
+  NIX_CFLAGS_COMPILE = toString [
+    # Can't say ${polkit.bin}/bin/pkttyagent here because that would
+    # lead to a cyclic dependency.
+    "-UPOLKIT_AGENT_BINARY_PATH" "-DPOLKIT_AGENT_BINARY_PATH=\"/run/current-system/sw/bin/pkttyagent\""
 
-      # Set the release_agent on /sys/fs/cgroup/systemd to the
-      # currently running systemd (/run/current-system/systemd) so
-      # that we don't use an obsolete/garbage-collected release agent.
-      "-USYSTEMD_CGROUP_AGENT_PATH" "-DSYSTEMD_CGROUP_AGENT_PATH=\"/run/current-system/systemd/lib/systemd/systemd-cgroups-agent\""
+    # Set the release_agent on /sys/fs/cgroup/systemd to the
+    # currently running systemd (/run/current-system/systemd) so
+    # that we don't use an obsolete/garbage-collected release agent.
+    "-USYSTEMD_CGROUP_AGENT_PATH" "-DSYSTEMD_CGROUP_AGENT_PATH=\"/run/current-system/systemd/lib/systemd/systemd-cgroups-agent\""
 
-      "-USYSTEMD_BINARY_PATH" "-DSYSTEMD_BINARY_PATH=\"/run/current-system/systemd/lib/systemd/systemd\""
-    ];
+    "-USYSTEMD_BINARY_PATH" "-DSYSTEMD_BINARY_PATH=\"/run/current-system/systemd/lib/systemd/systemd\""
+  ];
 
   doCheck = false; # fails a bunch of tests
 
diff --git a/pkgs/tools/misc/fontforge/default.nix b/pkgs/tools/misc/fontforge/default.nix
index e012d40271b5..6239e8395981 100644
--- a/pkgs/tools/misc/fontforge/default.nix
+++ b/pkgs/tools/misc/fontforge/default.nix
@@ -30,7 +30,7 @@ stdenv.mkDerivation rec {
   '';
 
   # do not use x87's 80-bit arithmetic, rouding errors result in very different font binaries
-  NIX_CFLAGS_COMPILE = lib.optionals stdenv.isi686 [ "-msse2" "-mfpmath=sse" ];
+  NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isi686 "-msse2 -mfpmath=sse";
 
   nativeBuildInputs = [ pkgconfig autoconf automake gnum4 libtool perl gettext ];
   buildInputs = [