diff -r 4c07b9c49b75 Lib/inspect.py
--- a/Lib/inspect.py	Mon Jun 18 15:37:31 2012 +0100
+++ b/Lib/inspect.py	Thu Jun 21 14:34:51 2012 -0700
@@ -577,7 +577,10 @@ def findsource(object):
         lnum = object.co_firstlineno - 1
         pat = re.compile(r'^(\s*def\s)|(.*(?<!\w)lambda(:|\s))|^(\s*@)')
         while lnum > 0:
-            if pat.match(lines[lnum]): break
+            try:
+                if pat.match(lines[lnum]): break
+            except IndexError:
+                raise IOError('could not get source code; invalid line number %d' % (lnum,))
             lnum = lnum - 1
         return lines, lnum
     raise IOError('could not find code object')
diff -r 4c07b9c49b75 Lib/test/inspect_fodder3.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Lib/test/inspect_fodder3.py	Thu Jun 21 14:34:51 2012 -0700
@@ -0,0 +1,1 @@
+# this file has one line
diff -r 4c07b9c49b75 Lib/test/test_inspect.py
--- a/Lib/test/test_inspect.py	Mon Jun 18 15:37:31 2012 +0100
+++ b/Lib/test/test_inspect.py	Thu Jun 21 14:34:51 2012 -0700
@@ -15,6 +15,7 @@ with check_py3k_warnings(
         quiet=True):
     from test import inspect_fodder as mod
     from test import inspect_fodder2 as mod2
+    from test import inspect_fodder3 as mod3
 
 # C module for test_findsource_binary
 import unicodedata
@@ -404,6 +405,14 @@ class TestBuggyCases(GetSourceBase):
         self.assertEqual(inspect.findsource(co), (lines,0))
         self.assertEqual(inspect.getsource(co), lines[0])
 
+    def test_findsource_code_with_line_number_out_of_range(self):
+        # mod3 is only a single line, but our source has multiple lines.
+        source = '\n\n1 // 0'
+        co = compile(source, mod3.__file__, "exec")
+        self.assertRaises(IOError, inspect.getsource, co)
+        self.assertRaises(IOError, inspect.findsource, co)
+
+
 
 class _BrokenDataDescriptor(object):
     """
diff -r 4c07b9c49b75 Misc/ACKS
--- a/Misc/ACKS	Mon Jun 18 15:37:31 2012 +0100
+++ b/Misc/ACKS	Thu Jun 21 14:34:51 2012 -0700
@@ -867,6 +867,7 @@ Laurence Tratt
 John Tromp
 Jason Trowbridge
 Anthony Tuininga
+Kevin Turner
 Stephen Turner
 Theodore Turocy
 Bill Tutt