diff --git a/pkgs/python-packages.nix b/pkgs/python-packages.nix
--- a/pkgs/python-packages.nix
+++ b/pkgs/python-packages.nix
@@ -913,13 +913,13 @@
     };
   };
   iso8601 = super.buildPythonPackage {
-    name = "iso8601-0.1.12";
+    name = "iso8601-0.1.11";
     buildInputs = with self; [];
     doCheck = false;
     propagatedBuildInputs = with self; [];
     src = fetchurl {
-      url = "https://files.pythonhosted.org/packages/45/13/3db24895497345fb44c4248c08b16da34a9eb02643cea2754b21b5ed08b0/iso8601-0.1.12.tar.gz";
-      sha256 = "49c4b20e1f38aa5cf109ddcd39647ac419f928512c869dc01d5c7098eddede82";
+      url = "https://files.pythonhosted.org/packages/c0/75/c9209ee4d1b5975eb8c2cba4428bde6b61bd55664a98290dd015cdb18e98/iso8601-0.1.11.tar.gz";
+      sha256 = "e8fb52f78880ae063336c94eb5b87b181e6a0cc33a6c008511bac9a6e980ef30";
     };
     meta = {
       license = [ pkgs.lib.licenses.mit ];
diff --git a/requirements.txt b/requirements.txt
--- a/requirements.txt
+++ b/requirements.txt
@@ -24,7 +24,7 @@ future==0.14.3
 futures==3.0.2
 gnureadline==6.3.8
 infrae.cache==1.0.1
-iso8601==0.1.12
+iso8601==0.1.11
 itsdangerous==0.24
 Jinja2==2.9.6
 billiard==3.5.0.3