diff --git a/_pytest/assertion.py b/_pytest/assertion.py
index 9c7143bb8..8f09e6661 100644
--- a/_pytest/assertion.py
+++ b/_pytest/assertion.py
@@ -50,8 +50,9 @@ except NameError:
 
 def pytest_assertrepr_compare(op, left, right):
     """return specialised explanations for some operators/operands"""
-    left_repr = py.io.saferepr(left, maxsize=30)
-    right_repr = py.io.saferepr(right, maxsize=30)
+    width = 80 - 15 - len(op) - 2 # 15 chars indentation, 1 space around op
+    left_repr = py.io.saferepr(left, maxsize=width/2)
+    right_repr = py.io.saferepr(right, maxsize=width-len(left_repr))
     summary = '%s %s %s' % (left_repr, op, right_repr)
 
     issequence = lambda x: isinstance(x, (list, tuple))
@@ -71,6 +72,9 @@ def pytest_assertrepr_compare(op, left, right):
             elif isdict(left) and isdict(right):
                 explanation = _diff_text(py.std.pprint.pformat(left),
                                          py.std.pprint.pformat(right))
+        elif op == 'not in':
+            if istext(left) and istext(right):
+                explanation = _notin_text(left, right)
     except py.builtin._sysex:
         raise
     except:
@@ -154,3 +158,11 @@ def _compare_eq_set(left, right):
         for item in diff_right:
             explanation.append(py.io.saferepr(item))
     return explanation
+
+
+def _notin_text(term, text):
+    index = text.find(term)
+    head = text[:index]
+    tail = text[index+len(term):]
+    correct_text = head + tail
+    return _diff_text(correct_text, text)
diff --git a/doc/example/assertion/failure_demo.py b/doc/example/assertion/failure_demo.py
index 74a2b3c70..c29323bc7 100644
--- a/doc/example/assertion/failure_demo.py
+++ b/doc/example/assertion/failure_demo.py
@@ -77,6 +77,22 @@ class TestSpecialisedExplanations(object):
     def test_in_list(self):
         assert 1 in [0, 2, 3, 4, 5]
 
+    def test_not_in_text_multiline(self):
+        text = 'some multiline\ntext\nwhich\nincludes foo\nand a\ntail'
+        assert 'foo' not in text
+
+    def test_not_in_text_single(self):
+        text = 'single foo line'
+        assert 'foo' not in text
+
+    def test_not_in_text_single_long(self):
+        text = 'head ' * 50 + 'foo ' + 'tail ' * 20
+        assert 'foo' not in text
+
+    def test_not_in_text_single_long_term(self):
+        text = 'head ' * 50 + 'f'*70 + 'tail ' * 20
+        assert 'f'*70 not in text
+
 
 def test_attribute():
     class Foo(object):
diff --git a/testing/test_assertion.py b/testing/test_assertion.py
index b4c74b0de..3cf76c19c 100644
--- a/testing/test_assertion.py
+++ b/testing/test_assertion.py
@@ -114,6 +114,11 @@ class TestAssert_reprcompare:
         expl = callequal(A(), '')
         assert not expl
 
+def test_reprcompare_notin():
+    detail = plugin.pytest_assertrepr_compare('not in', 'foo', 'aaafoobbb')[1:]
+    assert '- aaabbb' in detail
+    assert '+ aaafoobbb' in detail
+
 @needsnewassert
 def test_pytest_assertrepr_compare_integration(testdir):
     testdir.makepyfile("""