diff --git a/.gitignore b/.gitignore
index 4f032d1cbde..e282e507943 100644
--- a/.gitignore
+++ b/.gitignore
@@ -48,3 +48,6 @@ doc/*.fls
 doc/*.synctex.gz
 
 haddocks/
+
+# Visual Studio Code
+/.vscode
diff --git a/cabal.project b/cabal.project
index 4208b34ace4..9ff051443d1 100644
--- a/cabal.project
+++ b/cabal.project
@@ -1,4 +1,4 @@
-index-state: 2020-05-15T00:00:00Z
+index-state: 2020-07-15T00:00:00Z
 
 packages: ./typed-protocols
           ./typed-protocols-examples
diff --git a/nix/default.nix b/nix/default.nix
index ce28d95a88b..5f854721cdd 100644
--- a/nix/default.nix
+++ b/nix/default.nix
@@ -6,24 +6,25 @@
 let
   sources = import ./sources.nix { inherit pkgs; }
     // sourcesOverride;
-  iohkNix = import sources.iohk-nix {};
-  haskellNix = import sources."haskell.nix";
+  iohkNixMain = import sources.iohk-nix {};
+  haskellNix = (import sources."haskell.nix" { inherit system sourcesOverride; }).nixpkgsArgs;
   # use our own nixpkgs if it exists in our sources,
   # otherwise use iohkNix default nixpkgs.
   nixpkgs = if (sources ? nixpkgs)
     then (builtins.trace "Not using IOHK default nixpkgs (use 'niv drop nixpkgs' to use default for better sharing)"
       sources.nixpkgs)
-    else iohkNix.nixpkgs;
+    else (builtins.trace "Using IOHK default nixpkgs"
+      iohkNixMain.nixpkgs);
 
   # for inclusion in pkgs:
   overlays =
     # Haskell.nix (https://github.com/input-output-hk/haskell.nix)
     haskellNix.overlays
     # haskell-nix.haskellLib.extra: some useful extra utility functions for haskell.nix
-    ++ iohkNix.overlays.haskell-nix-extra
-    ++ iohkNix.overlays.crypto
+    ++ iohkNixMain.overlays.haskell-nix-extra
+    ++ iohkNixMain.overlays.crypto
     # iohkNix: nix utilities and niv:
-    ++ iohkNix.overlays.iohkNix
+    ++ iohkNixMain.overlays.iohkNix
     # our own overlays:
     ++ [
       (pkgs: _: with pkgs; {
diff --git a/nix/haskell.nix b/nix/haskell.nix
index 8898b71c94b..052d613e5bb 100644
--- a/nix/haskell.nix
+++ b/nix/haskell.nix
@@ -21,7 +21,10 @@ let
   };
 
   projectPackages = lib.attrNames (haskell-nix.haskellLib.selectProjectPackages
-    (haskell-nix.cabalProject { inherit src; }));
+    (haskell-nix.cabalProject {
+      inherit src;
+      compiler-nix-name = compiler;
+    }));
 
   # This creates the Haskell package set.
   # https://input-output-hk.github.io/haskell.nix/user-guide/projects/
diff --git a/nix/sources.json b/nix/sources.json
index 47f533e78f3..b2d8384f358 100644
--- a/nix/sources.json
+++ b/nix/sources.json
@@ -5,10 +5,10 @@
         "homepage": "https://input-output-hk.github.io/haskell.nix",
         "owner": "input-output-hk",
         "repo": "haskell.nix",
-        "rev": "59cf05606e7efbbc4741ae28fd8cc610cec94eb8",
-        "sha256": "1dpk49z97ld6a9ggy9ph6apk1ccgjwwnc4pzirh6galbcci4rqap",
+        "rev": "35b1ec8cd577bfc5abf7d0325f38aab01de5ed00",
+        "sha256": "0mg18i6g7nxd7qk0kaca6k8dsc3kam21772zlr19k03ff67ws55j",
         "type": "tarball",
-        "url": "https://github.com/input-output-hk/haskell.nix/archive/59cf05606e7efbbc4741ae28fd8cc610cec94eb8.tar.gz",
+        "url": "https://github.com/input-output-hk/haskell.nix/archive/35b1ec8cd577bfc5abf7d0325f38aab01de5ed00.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "iohk-nix": {
@@ -17,10 +17,10 @@
         "homepage": null,
         "owner": "input-output-hk",
         "repo": "iohk-nix",
-        "rev": "6bd8f364080529ab9b9776e081085819624a4f3a",
-        "sha256": "0n17wl45hhqcrxlhb7f5xk8ln2k2nv8fqmx81ffnvjjfrfzdpfkm",
+        "rev": "95f7dfdff554223606f6be266c36eabe81cbe800",
+        "sha256": "05ibcw52jg7q66sd0vqj0fv3zlz7mdrfywys9111n4bj9rd9rl1n",
         "type": "tarball",
-        "url": "https://github.com/input-output-hk/iohk-nix/archive/6bd8f364080529ab9b9776e081085819624a4f3a.tar.gz",
+        "url": "https://github.com/input-output-hk/iohk-nix/archive/95f7dfdff554223606f6be266c36eabe81cbe800.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "niv": {
diff --git a/nix/sources.nix b/nix/sources.nix
index 8a725cb4e7f..954ba5a6b64 100644
--- a/nix/sources.nix
+++ b/nix/sources.nix
@@ -12,11 +12,16 @@ let
     else
       pkgs.fetchurl { inherit (spec) url sha256; };
 
-  fetch_tarball = pkgs: spec:
-    if spec.builtin or true then
-      builtins_fetchTarball { inherit (spec) url sha256; }
-    else
-      pkgs.fetchzip { inherit (spec) url sha256; };
+  fetch_tarball = pkgs: name: spec:
+    let
+      ok = str: ! builtins.isNull (builtins.match "[a-zA-Z0-9+-._?=]" str);
+      # sanitize the name, though nix will still fail if name starts with period
+      name' = stringAsChars (x: if ! ok x then "-" else x) "${name}-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchTarball { name = name'; inherit (spec) url sha256; }
+      else
+        pkgs.fetchzip { name = name'; inherit (spec) url sha256; };
 
   fetch_git = spec:
     builtins.fetchGit { url = spec.repo; inherit (spec) rev ref; };
@@ -72,10 +77,10 @@ let
     if ! builtins.hasAttr "type" spec then
       abort "ERROR: niv spec ${name} does not have a 'type' attribute"
     else if spec.type == "file" then fetch_file pkgs spec
-    else if spec.type == "tarball" then fetch_tarball pkgs spec
+    else if spec.type == "tarball" then fetch_tarball pkgs name spec
     else if spec.type == "git" then fetch_git spec
-    else if spec.type == "builtin-tarball" then fetch_builtin-tarball spec
-    else if spec.type == "builtin-url" then fetch_builtin-url spec
+    else if spec.type == "builtin-tarball" then fetch_builtin-tarball name
+    else if spec.type == "builtin-url" then fetch_builtin-url name
     else
       abort "ERROR: niv spec ${name} has unknown type ${builtins.toJSON spec.type}";
 
@@ -87,13 +92,23 @@ let
     listToAttrs (map (attr: { name = attr; value = f attr set.${attr}; }) (attrNames set))
   );
 
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/lists.nix#L295
+  range = first: last: if first > last then [] else builtins.genList (n: first + n) (last - first + 1);
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L257
+  stringToCharacters = s: map (p: builtins.substring p 1 s) (range 0 (builtins.stringLength s - 1));
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L269
+  stringAsChars = f: s: concatStrings (map f (stringToCharacters s));
+  concatStrings = builtins.concatStringsSep "";
+
   # fetchTarball version that is compatible between all the versions of Nix
-  builtins_fetchTarball = { url, sha256 }@attrs:
+  builtins_fetchTarball = { url, name, sha256 }@attrs:
     let
       inherit (builtins) lessThan nixVersion fetchTarball;
     in
       if lessThan nixVersion "1.12" then
-        fetchTarball { inherit url; }
+        fetchTarball { inherit name url; }
       else
         fetchTarball attrs;