diff --git a/Lib/test/test_posix.py b/Lib/test/test_posix.py
index 233fea4d57bbb0..1cd9e567b36e56 100644
--- a/Lib/test/test_posix.py
+++ b/Lib/test/test_posix.py
@@ -1375,6 +1375,7 @@ def test_sched_setaffinity(self):
         self.assertEqual(posix.sched_getaffinity(0), mask)
         self.assertRaises(OSError, posix.sched_setaffinity, 0, [])
         self.assertRaises(ValueError, posix.sched_setaffinity, 0, [-10])
+        self.assertRaises(ValueError, posix.sched_setaffinity, 0, map(int, "0X"))
         self.assertRaises(OverflowError, posix.sched_setaffinity, 0, [1<<128])
         self.assertRaises(OSError, posix.sched_setaffinity, -1, mask)
 
diff --git a/Misc/NEWS.d/next/Library/2019-06-26-22-25-05.bpo-37420.CxFJ09.rst b/Misc/NEWS.d/next/Library/2019-06-26-22-25-05.bpo-37420.CxFJ09.rst
new file mode 100644
index 00000000000000..dea1a292501449
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-06-26-22-25-05.bpo-37420.CxFJ09.rst
@@ -0,0 +1,2 @@
+:func:`os.sched_setaffinity` now correctly handles errors that arise during iteration over its ``mask`` argument.
+Patch by Brandt Bucher.
\ No newline at end of file
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index b758e766a4d07a..58cb9b0d468d2f 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -5809,6 +5809,9 @@ os_sched_setaffinity_impl(PyObject *module, pid_t pid, PyObject *mask)
         }
         CPU_SET_S(cpu, setsize, cpu_set);
     }
+    if (PyErr_Occurred()) {
+        goto error;
+    }
     Py_CLEAR(iterator);
 
     if (sched_setaffinity(pid, setsize, cpu_set)) {