diff --git a/.travis.yml b/.travis.yml
index 13ca60c..a74d999 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -21,6 +21,7 @@ env:
   jobs:
   - TestModules=1 STABLE=1
   - PKG=hwi STABLE=1
+  - PKG=hwi STABLE=0
   - PKG=lightning-charge STABLE=1
   - PKG=lightning-charge STABLE=0
   - PKG=nanopos STABLE=1
diff --git a/pkgs/hwi/default.nix b/pkgs/hwi/default.nix
index 9377158..41ec2d5 100644
--- a/pkgs/hwi/default.nix
+++ b/pkgs/hwi/default.nix
@@ -1,12 +1,18 @@
 { stdenv, fetchurl, fetchFromGitHub, python3 }:
 
 with stdenv.lib;
-with python3.pkgs;
 
 let
-  buildInputs = [ mnemonic ecdsa typing-extensions hidapi libusb1 pyaes ];
+  python = python3.override {
+    packageOverrides = self: super: {
+      # HWI requires mnemonic <0.19 but nixpkgs has a newer version
+      mnemonic = self.callPackage ./mnemonic {};
+      # HWI requires ecdsa <0.14 but nixpkgs has a newer version
+      ecdsa = self.callPackage ./ecdsa {};
+    };
+  };
 in
-buildPythonPackage rec {
+python.pkgs.buildPythonPackage rec {
   pname = "hwi";
   version = "1.0.3";
 
@@ -20,8 +26,7 @@ buildPythonPackage rec {
   # TODO: enable tests
   doCheck = false;
 
-  inherit buildInputs;
-  propagatedBuildInputs = buildInputs;
+  propagatedBuildInputs = with python.pkgs; [ mnemonic ecdsa typing-extensions hidapi libusb1 pyaes ];
 
   meta = with lib; {
     homepage = https://github.com/bitcoin-core/hwi;
diff --git a/pkgs/hwi/ecdsa/default.nix b/pkgs/hwi/ecdsa/default.nix
new file mode 100644
index 0000000..d9c43f5
--- /dev/null
+++ b/pkgs/hwi/ecdsa/default.nix
@@ -0,0 +1,28 @@
+{ stdenv
+, buildPythonPackage
+, fetchPypi
+, pkgs
+, six
+}:
+
+buildPythonPackage rec {
+  pname = "ecdsa";
+  version = "0.13.3";
+
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "163c80b064a763ea733870feb96f9dd9b92216cfcacd374837af18e4e8ec3d4d";
+  };
+
+  propagatedBuildInputs = [ six ];
+  # Only needed for tests
+  checkInputs = [ pkgs.openssl ];
+
+  meta = with stdenv.lib; {
+    description = "ECDSA cryptographic signature library";
+    homepage = "https://github.com/warner/python-ecdsa";
+    license = licenses.mit;
+    maintainers = with maintainers; [ aszlig ];
+  };
+
+}
diff --git a/pkgs/hwi/mnemonic/default.nix b/pkgs/hwi/mnemonic/default.nix
new file mode 100644
index 0000000..4cb416a
--- /dev/null
+++ b/pkgs/hwi/mnemonic/default.nix
@@ -0,0 +1,20 @@
+{ lib, fetchPypi, buildPythonPackage, pbkdf2 }:
+
+buildPythonPackage rec {
+  pname = "mnemonic";
+  version = "0.18";
+
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "02a7306a792370f4a0c106c2cf1ce5a0c84b9dbd7e71c6792fdb9ad88a727f1d";
+  };
+
+  propagatedBuildInputs = [ pbkdf2 ];
+
+  meta = {
+    description = "Implementation of Bitcoin BIP-0039";
+    homepage = "https://github.com/trezor/python-mnemonic";
+    license = lib.licenses.mit;
+    maintainers = with lib.maintainers; [ np ];
+  };
+}