diff --git a/Lib/fnmatch.py b/Lib/fnmatch.py
index 4c149eb7817..b1c37f59dff 100644
--- a/Lib/fnmatch.py
+++ b/Lib/fnmatch.py
@@ -15,6 +15,7 @@ import re
 __all__ = ["filter", "fnmatch","fnmatchcase","translate"]
 
 _cache = {}
+_MAXCACHE = 100
 
 def fnmatch(name, pat):
     """Test whether FILENAME matches PATTERN.
@@ -44,6 +45,8 @@ def filter(names, pat):
     pat=os.path.normcase(pat)
     if not pat in _cache:
         res = translate(pat)
+        if len(_cache) >= _MAXCACHE:
+            _cache.clear()
         _cache[pat] = re.compile(res)
     match=_cache[pat].match
     if os.path is posixpath:
@@ -66,6 +69,8 @@ def fnmatchcase(name, pat):
 
     if not pat in _cache:
         res = translate(pat)
+        if len(_cache) >= _MAXCACHE:
+            _cache.clear()
         _cache[pat] = re.compile(res)
     return _cache[pat].match(name) is not None
 
diff --git a/Lib/test/test_fnmatch.py b/Lib/test/test_fnmatch.py
index 3a55b85f623..015c580b61f 100644
--- a/Lib/test/test_fnmatch.py
+++ b/Lib/test/test_fnmatch.py
@@ -3,7 +3,7 @@
 from test import test_support
 import unittest
 
-from fnmatch import fnmatch, fnmatchcase
+from fnmatch import fnmatch, fnmatchcase, _MAXCACHE, _cache
 
 
 class FnmatchTestCase(unittest.TestCase):
@@ -49,6 +49,15 @@ class FnmatchTestCase(unittest.TestCase):
         check('AbC', 'abc', 0, fnmatchcase)
         check('abc', 'AbC', 0, fnmatchcase)
 
+    def test_cache_clearing(self):
+        # check that caches do not grow too large
+        # http://bugs.python.org/issue7846
+
+        # string pattern cache
+        for i in range(_MAXCACHE + 1):
+            fnmatch('foo', '?' * i)
+
+        self.assertTrue(len(_cache) <= _MAXCACHE)
 
 def test_main():
     test_support.run_unittest(FnmatchTestCase)
diff --git a/Misc/ACKS b/Misc/ACKS
index 94a22a860ec..b6634a789b7 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -132,6 +132,7 @@ Tom Christiansen
 Vadim Chugunov
 David Cinege
 Mike Clarkson
+Andrew Clegg
 Brad Clements
 Steve Clift
 Nick Coghlan
diff --git a/Misc/NEWS b/Misc/NEWS
index 0efac1b772a..f6f8044ac80 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -81,6 +81,8 @@ C-API
 Library
 -------
 
+- Issue #7646: The fnmatch pattern cache no longer grows without bound.
+
 - Issue #9136: Fix 'dictionary changed size during iteration'
   RuntimeError produced when profiling the decimal module.  This was
   due to a dangerous iteration over 'locals()' in Context.__init__.