diff --git a/pkgs/applications/networking/browsers/firefox/4.0.nix b/pkgs/applications/networking/browsers/firefox/4.0.nix
index f9aae02c32ff..c7b40078d243 100644
--- a/pkgs/applications/networking/browsers/firefox/4.0.nix
+++ b/pkgs/applications/networking/browsers/firefox/4.0.nix
@@ -11,7 +11,7 @@
   enableOfficialBranding ? false
 }:
 
-assert stdenv.gcc ? libc;
+assert stdenv.gcc ? libc && stdenv.gcc.libc != null;
 
 rec {
 
diff --git a/pkgs/development/guile-modules/guile-lib/default.nix b/pkgs/development/guile-modules/guile-lib/default.nix
index cfcef5f05518..b885d446206c 100644
--- a/pkgs/development/guile-modules/guile-lib/default.nix
+++ b/pkgs/development/guile-modules/guile-lib/default.nix
@@ -1,5 +1,7 @@
 {stdenv, fetchurl, guile, texinfo}:
 
+assert stdenv ? gcc && stdenv.gcc ? gcc && stdenv.gcc.gcc != null;
+
 stdenv.mkDerivation rec {
   name = "guile-lib-0.2.0";
 
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 0ac77a402d3d..84b041b1d5d4 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -6315,7 +6315,7 @@ let
   icecat4Xul =
     (symlinkJoin "icecat-with-xulrunner-${icecat4.version}"
        [ icecat4 icecatXulrunner4 ])
-    // { inherit (icecat4) gtk isFirefox4Like meta; };
+    // { inherit (icecat4) gtk meta; };
 
   icecat4Wrapper = wrapFirefox icecat4Xul "icecat" "";