diff --git a/src/sortedcontainers/sorteddict.py b/src/sortedcontainers/sorteddict.py
index 273c9ce..4e37615 100644
--- a/src/sortedcontainers/sorteddict.py
+++ b/src/sortedcontainers/sorteddict.py
@@ -497,16 +497,16 @@ def update(self, *args, **kwargs):
         :param kwargs: keyword arguments mapping
 
         """
-        if not self:
-            dict.update(self, *args, **kwargs)
-            self._list_update(dict.__iter__(self))
-            return
-
         if not kwargs and len(args) == 1 and isinstance(args[0], dict):
             pairs = args[0]
         else:
             pairs = dict(*args, **kwargs)
 
+        if not self:
+            dict.update(self, pairs)
+            self._list_update(dict.__iter__(self))
+            return
+
         if (10 * len(pairs)) > len(self):
             dict.update(self, pairs)
             self._list_clear()
diff --git a/tests/test_coverage_sorteddict.py b/tests/test_coverage_sorteddict.py
index ad59290..1206686 100644
--- a/tests/test_coverage_sorteddict.py
+++ b/tests/test_coverage_sorteddict.py
@@ -582,3 +582,29 @@ def test_ior():
     temp2 = SortedDict(mapping[13:])
     temp1 |= temp2
     assert temp1 == dict(mapping)
+
+
+@pytest.mark.parametrize('initial', [{}, {'existing': 0}])
+@pytest.mark.parametrize('key', [None, len])
+def test_update_malformed_pairs_preserves_index(initial, key):
+    temp = SortedDict(key, initial)
+    with pytest.raises(ValueError):
+        temp.update([('valid', 1), ('invalid',)])
+    temp._check()
+    assert dict(temp.items()) == initial
+    temp['next'] = 2
+    temp._check()
+    assert temp.pop('next') == 2
+
+
+@pytest.mark.parametrize('initial', [{}, {'existing': 0}])
+def test_update_failing_iterator_preserves_index(initial):
+    def pairs():
+        yield 'valid', 1
+        raise RuntimeError('source failed')
+
+    temp = SortedDict(initial)
+    with pytest.raises(RuntimeError, match='source failed'):
+        temp.update(pairs())
+    temp._check()
+    assert dict(temp.items()) == initial