diff --git a/pkgs/applications/networking/instant-messengers/baresip/default.nix b/pkgs/applications/networking/instant-messengers/baresip/default.nix
index 00b82d555fe..ba530374c71 100644
--- a/pkgs/applications/networking/instant-messengers/baresip/default.nix
+++ b/pkgs/applications/networking/instant-messengers/baresip/default.nix
@@ -19,8 +19,6 @@ stdenv.mkDerivation rec {
     "LIBRE_INC=${libre}/include/re"
     "LIBRE_SO=${libre}/lib"
     "LIBREM_PATH=${librem}"
-    "SYSROOT=${stdenv.gcc.libc}"
-    "SYSROOT_ALT=${stdenv.gcc.gcc}"
     ''PREFIX=$(out)''
     "USE_VIDEO=1"
 
@@ -33,7 +31,10 @@ stdenv.mkDerivation rec {
 
     "USE_BV32=" "USE_COREAUDIO=" "USE_G711=" "USE_G722=" "USE_G722_1=" 
     "USE_ILBC=" "USE_OPUS=" "USE_SILK=" 
-  ];
+  ]
+  ++ stdenv.lib.optional (stdenv.gcc.gcc != null) "SYSROOT_ALT=${stdenv.gcc.gcc}"
+  ++ stdenv.lib.optional (stdenv.gcc.libc != null) "SYSROOT=${stdenv.gcc.libc}"
+  ;
   NIX_CFLAGS_COMPILE='' -I${librem}/include/rem -I${gsm}/include/gsm '';
   meta = {
     homepage = "http://www.creytiv.com/baresip.html";
diff --git a/pkgs/development/libraries/libre/default.nix b/pkgs/development/libraries/libre/default.nix
index 208744fcdde..cc9139d664e 100644
--- a/pkgs/development/libraries/libre/default.nix
+++ b/pkgs/development/libraries/libre/default.nix
@@ -9,10 +9,11 @@ stdenv.mkDerivation rec {
   buildInputs = [zlib openssl];
   makeFlags = [
     "USE_ZLIB=1" "USE_OPENSSL=1" 
-    "SYSROOT=${stdenv.gcc.libc}"
-    "SYSROOT_ALT=${stdenv.gcc.gcc}"
     ''PREFIX=$(out)''
-  ];
+  ]
+  ++ stdenv.lib.optional (stdenv.gcc.gcc != null) "SYSROOT_ALT=${stdenv.gcc.gcc}"
+  ++ stdenv.lib.optional (stdenv.gcc.libc != null) "SYSROOT=${stdenv.gcc.libc}"
+  ;
   meta = {
     homepage = "http://www.creytiv.com/re.html";
     platforms = with stdenv.lib.platforms; linux;
diff --git a/pkgs/development/libraries/librem/.default.nix.swp b/pkgs/development/libraries/librem/.default.nix.swp
deleted file mode 100644
index ad2094919ae..00000000000
Binary files a/pkgs/development/libraries/librem/.default.nix.swp and /dev/null differ
diff --git a/pkgs/development/libraries/librem/default.nix b/pkgs/development/libraries/librem/default.nix
index e6b22d1ab4d..04f3cc97bf3 100644
--- a/pkgs/development/libraries/librem/default.nix
+++ b/pkgs/development/libraries/librem/default.nix
@@ -10,10 +10,11 @@ stdenv.mkDerivation rec {
   makeFlags = [
     "LIBRE_MK=${libre}/share/re/re.mk"
     "LIBRE_INC=${libre}/include/re"
-    "SYSROOT=${stdenv.gcc.libc}"
-    "SYSROOT_ALT=${stdenv.gcc.gcc}"
     ''PREFIX=$(out)''
-  ];
+  ]
+  ++ stdenv.lib.optional (stdenv.gcc.gcc != null) "SYSROOT_ALT=${stdenv.gcc.gcc}"
+  ++ stdenv.lib.optional (stdenv.gcc.libc != null) "SYSROOT=${stdenv.gcc.libc}"
+  ;
   meta = {
     homepage = "http://www.creytiv.com/rem.html";
     platforms = with stdenv.lib.platforms; linux;