diff --git a/pkgs/development/python-modules/binaryornot/default.nix b/pkgs/development/python-modules/binaryornot/default.nix
new file mode 100644
index 000000000000..2f0b01a5c23d
--- /dev/null
+++ b/pkgs/development/python-modules/binaryornot/default.nix
@@ -0,0 +1,27 @@
+{ lib, buildPythonPackage, fetchPypi, chardet, hypothesis }:
+
+buildPythonPackage rec {
+  pname = "binaryornot";
+  version = "0.4.4";
+
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "359501dfc9d40632edc9fac890e19542db1a287bbcfa58175b66658392018061";
+  };
+
+  prePatch = ''
+    # See https://github.com/audreyr/binaryornot/issues/40
+    substituteInPlace tests/test_check.py \
+      --replace "average_size=512" "average_size=128"
+  '';
+
+  propagatedBuildInputs = [ chardet ];
+
+  checkInputs = [ hypothesis ];
+
+  meta = with lib; {
+    homepage = https://github.com/audreyr/binaryornot;
+    description = "Ultra-lightweight pure Python package to check if a file is binary or text";
+    license = licenses.bsd3;
+  };
+}
diff --git a/pkgs/top-level/python-packages.nix b/pkgs/top-level/python-packages.nix
index 8c2317ffa0eb..af1df92efda2 100644
--- a/pkgs/top-level/python-packages.nix
+++ b/pkgs/top-level/python-packages.nix
@@ -1671,27 +1671,7 @@ in {
     };
   };
 
-
-  binaryornot = buildPythonPackage rec {
-    name = "binaryornot-${version}";
-    version = "0.4.0";
-
-    src = pkgs.fetchurl {
-      url ="mirror://pypi/b/binaryornot/${name}.tar.gz";
-      sha256 = "1j4f51dxic39mdwf6alj7gd769wy6mhk916v031wjali51xkh3xb";
-    };
-
-    buildInputs = with self; [ hypothesis ];
-
-    propagatedBuildInputs = with self; [ chardet ];
-
-    meta = {
-      homepage = https://github.com/audreyr/binaryornot;
-      description = "Ultra-lightweight pure Python package to check if a file is binary or text";
-      license = licenses.bsd3;
-    };
-  };
-
+  binaryornot = callPackage ../development/python-modules/binaryornot { };
 
   bitbucket_api = buildPythonPackage rec {
     name = "bitbucket-api-0.4.4";