diff --git a/parso/python/diff.py b/parso/python/diff.py
index ac11f31..c88b9c9 100644
--- a/parso/python/diff.py
+++ b/parso/python/diff.py
@@ -676,9 +676,7 @@ class _NodesTree(object):
                 # line, otherwise it's going to be missing. This happens e.g.
                 # if a bracket is around before that moves newlines to
                 # prefixes.
-                newline_index = max(p.rfind('\n'), p.rfind('\r'))
-                if newline_index > -1:
-                    new_prefix = p[:newline_index + 1]
+                new_prefix = split_lines(p, keepends=True)[0]
 
             if had_valid_suite_last:
                 last = new_nodes[-1]
diff --git a/test/test_diff_parser.py b/test/test_diff_parser.py
index 91ccedd..6f526aa 100644
--- a/test/test_diff_parser.py
+++ b/test/test_diff_parser.py
@@ -1214,3 +1214,30 @@ def test_open_bracket(differ):
     differ.parse(code2, copies=1, parsers=1, expect_error_leaves=True)
     differ.parse(code3, copies=1, parsers=1, expect_error_leaves=True)
     differ.parse(code1, copies=1, parsers=1)
+
+
+def test_aaaaaaaaaa(differ):
+    code1 = dedent('''\
+        class C:
+            def f(self):
+                (
+                b
+                c
+
+            def g(self):
+                d
+        ''')
+    code2 = dedent('''\
+        class C:
+            def f(self):
+                (
+                b
+                c
+                self.
+
+            def g(self):
+                d
+        ''')
+    differ.initialize(code1)
+    differ.parse(code2, copies=1, parsers=2, expect_error_leaves=True)
+    differ.parse(code1, copies=2, parsers=0, expect_error_leaves=True)