diff --git a/build.sh b/build.sh
index 41ba821..2909a82 100755
--- a/build.sh
+++ b/build.sh
@@ -109,8 +109,7 @@ if [ "$GHCVERSION" = "ghcjs" ]
       --arg buildStackProject "$buildStackProject" \
       "$generateOptparseApplicativeCompletion" \
       --arg allowInconsistentDependencies "$allowInconsistentDependencies" \
-      ghcjs \
-      "$@"
+      ghcjs
 
   else
 
@@ -134,14 +133,26 @@ if [ "$GHCVERSION" = "ghcjs" ]
       --arg disableOptimization "$disableOptimization" \
       --arg buildStackProject "$buildStackProject" \
       "$generateOptparseApplicativeCompletion" \
-      --arg allowInconsistentDependencies "$allowInconsistentDependencies" \
-      "$@"
+      --arg allowInconsistentDependencies "$allowInconsistentDependencies"
 
 fi
 }
 
 MAIN() {
 
+
+#  2020-06-01: NOTE: Nix installer installs old Nix version that has bugs that prevented importing Nixpks repository channels, updating to latest Nix since it does not have that bug
+# NOTE: Overall it is useful to have in CI test builds the latest stable Nix
+# NOTE: User-run update for Linux setup
+nix upgrade-nix || true
+# NOTE: Superuser update for macOS setup
+sudo nix upgrade-nix || true
+
+# NOTE: Make channels current
+nix-channel --update || true
+sudo nix-channel --update || true
+
+
 # NOTE: Secrets are not shared to PRs from forks
 # NOTE: nix-build | cachix push <name> - uploads binaries, runs&works only in the branches of the main repository, so for PRs - else case runs
 
diff --git a/default.nix b/default.nix
index c7846e9..a843da9 100644
--- a/default.nix
+++ b/default.nix
@@ -29,17 +29,21 @@
 
 , withHoogle  ? true
 
-, rev ? "29d57de30101b51b016310ee51c2c4ec762f88db" #  2020-05-23: NOTE: UTC 17:00
 
-, sha256 ? "1wjljkffb3gzdvpfc4v98mrhzack6k9i7860n8cf5nipyab6jbq9"
+, useRev ? false
+# Accepts Nixpkgs channel name and Git revision
+, rev ? "nixpkgs-unstable"
 
 , pkgs ?
     if builtins.compareVersions builtins.nixVersion "2.0" < 0
     then abort "hnix requires at least nix 2.0"
-    else import (builtins.fetchTarball {
-           url = "https://github.com/NixOS/nixpkgs/archive/${rev}.tar.gz";
-           inherit sha256; }) {
-      config.allowBroken = true;
+    else
+      if useRev
+        then import (builtins.fetchTarball "https://github.com/NixOS/nixpkgs/archive/${rev}.tar.gz") {}
+      # Please not guard with hash, so we able to use current channels (rolling `rev`) of Haskell&Nixpkgs
+        else import <nixpkgs> {}
+      // {
+        config.allowBroken = true;
       # config.packageOverrides = pkgs: rec {
       #   nix = pkgs.nixStable.overrideDerivation (attrs: with pkgs; rec {
       #     src = if builtins.pathExists ./data/nix/.version
@@ -76,7 +80,7 @@
       #     outputs = builtins.filter (s: s != "doc" && s != "man" ) attrs.outputs;
       #   });
       # };
-    }
+      }
 
 , mkDerivation   ? null
 }: