diff --git a/pkgs/development/python-modules/nmigen/default.nix b/pkgs/development/python-modules/nmigen/default.nix
index 02569e0a81bf..8269c07cba0e 100644
--- a/pkgs/development/python-modules/nmigen/default.nix
+++ b/pkgs/development/python-modules/nmigen/default.nix
@@ -8,28 +8,23 @@
 , bitarray
 , jinja2
 
-# nmigen.{test,build} call out to these
+# for tests
 , yosys
 , symbiyosys
-, nextpnr ? null
-, icestorm ? null
-, trellis ? null
-
-# for tests
 , yices
 }:
 
 buildPythonPackage rec {
   pname = "nmigen";
-  version = "unstable-2019-09-28";
+  version = "unstable-2019-10-17";
   # python setup.py --version
-  realVersion = "0.1.dev689+g${lib.substring 0 7 src.rev}";
+  realVersion = "0.1.rc2.dev5+g${lib.substring 0 7 src.rev}";
 
   src = fetchFromGitHub {
     owner = "m-labs";
     repo = "nmigen";
-    rev = "a02e3750bfeba44bcaad4c5de8d9eb0ef055d9c6";
-    sha256 = "0m399c2nm7y54q2f0fbkmi4h35csbc2llckm6k9kqdf5qc6355wd";
+    rev = "9fba5ccb513cfbd53f884b1efca699352d2471b9";
+    sha256 = "02bjry4sqjsrhl0s42zl1zl06gk5na9i6br6vmz7fvxic29vl83v";
   };
 
   disabled = pythonOlder "3.6";
@@ -38,25 +33,7 @@ buildPythonPackage rec {
 
   propagatedBuildInputs = [ setuptools pyvcd bitarray jinja2 ];
 
-  checkInputs = [ yosys yices ];
-
-  postPatch = let
-    tool = pkg: name:
-      if pkg == null then {} else { ${name} = "${pkg}/bin/${name}"; };
-
-    # Only FOSS toolchain supported out of the box, sorry!
-    toolchainOverrides =
-      tool yosys "yosys" //
-      tool symbiyosys "sby" //
-      tool nextpnr "nextpnr-ice40" //
-      tool nextpnr "nextpnr-ecp5" //
-      tool icestorm "icepack" //
-      tool trellis "ecppack";
-  in ''
-    substituteInPlace nmigen/_toolchain.py \
-      --replace 'overrides = {}' \
-                'overrides = ${builtins.toJSON toolchainOverrides}'
-  '';
+  checkInputs = [ yosys symbiyosys yices ];
 
   preBuild = ''
     export SETUPTOOLS_SCM_PRETEND_VERSION="${realVersion}"