diff --git a/CHANGELOG b/CHANGELOG
index 8fe13a643..07da9a1e4 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -3,6 +3,9 @@ NEXT
 
 - fixed issue561: adapt autouse fixture example for python3.
 
+- fixed issue453: assertion rewriting issue with __repr__ containing
+  "\n{", "\n}" and "\n~".
+
 - Fix example in monkeypatch documentation, thanks t-8ch.
 
 - Do not mark as universal wheel because Python 2.6 is different from
diff --git a/_pytest/assertion/rewrite.py b/_pytest/assertion/rewrite.py
index 523d2b2dc..cb8acc187 100644
--- a/_pytest/assertion/rewrite.py
+++ b/_pytest/assertion/rewrite.py
@@ -326,7 +326,25 @@ def rewrite_asserts(mod):
     AssertionRewriter().run(mod)
 
 
-_saferepr = py.io.saferepr
+def _saferepr(obj):
+    """Get a safe repr of an object for assertion error messages.
+
+    The assertion formatting (util.format_explanation()) requires
+    newlines to be escaped since they are a special character for it.
+    Normally assertion.util.format_explanation() does this but for a
+    custom repr it is possible to contain one of the special escape
+    sequences, especially '\n{' and '\n}' are likely to be present in
+    JSON reprs.
+
+    """
+    repr = py.io.saferepr(obj)
+    if py.builtin._istext(repr):
+        t = py.builtin.text
+    else:
+        t = py.builtin.bytes
+    return repr.replace(t("\n"), t("\\n"))
+
+
 from _pytest.assertion.util import format_explanation as _format_explanation # noqa
 
 def _should_repr_global_name(obj):
diff --git a/testing/test_assertrewrite.py b/testing/test_assertrewrite.py
index 72e2d4e10..7e0cfbf83 100644
--- a/testing/test_assertrewrite.py
+++ b/testing/test_assertrewrite.py
@@ -313,6 +313,17 @@ class TestAssertionRewrite:
             assert "%test" == "test"
         assert getmsg(f).startswith("assert '%test' == 'test'")
 
+    def test_custom_repr(self):
+        def f():
+            class Foo(object):
+                a = 1
+
+                def __repr__(self):
+                    return "\n{ \n~ \n}"
+            f = Foo()
+            assert 0 == f.a
+        assert r"where 1 = \n{ \n~ \n}.a" in util._format_lines([getmsg(f)])[0]
+
 
 class TestRewriteOnImport: