diff --git a/Lib/test/test_bytes.py b/Lib/test/test_bytes.py
index 9b5f713b0b8..c04f7b305a0 100644
--- a/Lib/test/test_bytes.py
+++ b/Lib/test/test_bytes.py
@@ -116,8 +116,8 @@ class BaseBytesTest(unittest.TestCase):
         a = self.type2test(b"\x01\x02\x03")
         self.assertEqual(a, b"\x01\x02\x03")
 
-        # http://bugs.python.org/issue29159
-        # Fallback when __index__ raises exception other than OverflowError
+        # Issues #29159 and #34974.
+        # Fallback when __index__ raises a TypeError
         class B(bytes):
             def __index__(self):
                 raise TypeError
@@ -156,6 +156,20 @@ class BaseBytesTest(unittest.TestCase):
         self.assertRaises(ValueError, self.type2test, [sys.maxint+1])
         self.assertRaises(ValueError, self.type2test, [10**100])
 
+    def test_constructor_exceptions(self):
+        # Issue #34974: bytes and bytearray constructors replace unexpected
+        # exceptions.
+        class BadInt:
+            def __index__(self):
+                1/0
+        self.assertRaises(ZeroDivisionError, self.type2test, BadInt())
+        self.assertRaises(ZeroDivisionError, self.type2test, [BadInt()])
+
+        class BadIterable:
+            def __iter__(self):
+                1/0
+        self.assertRaises(ZeroDivisionError, self.type2test, BadIterable())
+
     def test_compare(self):
         b1 = self.type2test([1, 2, 3])
         b2 = self.type2test([1, 2, 3])
diff --git a/Misc/NEWS.d/next/Core and Builtins/2018-10-13-22-24-19.bpo-34974.7LgTc2.rst b/Misc/NEWS.d/next/Core and Builtins/2018-10-13-22-24-19.bpo-34974.7LgTc2.rst
new file mode 100644
index 00000000000..34e6273db94
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2018-10-13-22-24-19.bpo-34974.7LgTc2.rst	
@@ -0,0 +1,3 @@
+The :class:`bytearray` constructor no longer convert
+unexpected exceptions (e.g. :exc:`MemoryError` and :exc:`KeyboardInterrupt`)
+to :exc:`TypeError`.
diff --git a/Objects/bytearrayobject.c b/Objects/bytearrayobject.c
index c178d9ef65d..a96d6d981dd 100644
--- a/Objects/bytearrayobject.c
+++ b/Objects/bytearrayobject.c
@@ -41,8 +41,10 @@ _getbytevalue(PyObject* arg, int *value)
     else {
         PyObject *index = PyNumber_Index(arg);
         if (index == NULL) {
-            PyErr_Format(PyExc_TypeError,
-                         "an integer or string of size 1 is required");
+            if (PyErr_ExceptionMatches(PyExc_TypeError)) {
+                PyErr_Format(PyExc_TypeError,
+                             "an integer or string of size 1 is required");
+            }
             return 0;
         }
         face_value = PyLong_AsLong(index);
@@ -852,7 +854,7 @@ bytearray_init(PyByteArrayObject *self, PyObject *args, PyObject *kwds)
     /* Is it an int? */
     count = PyNumber_AsSsize_t(arg, PyExc_OverflowError);
     if (count == -1 && PyErr_Occurred()) {
-        if (PyErr_ExceptionMatches(PyExc_OverflowError))
+        if (!PyErr_ExceptionMatches(PyExc_TypeError))
             return -1;
         PyErr_Clear();
     }