diff --git a/httplib2/__init__.py b/httplib2/__init__.py
index fd4c768..6ad8afe 100644
--- a/httplib2/__init__.py
+++ b/httplib2/__init__.py
@@ -82,6 +82,7 @@
 class FailedToDecompressContent(HttpLib2Error): pass
 class UnimplementedDigestAuthOptionError(HttpLib2Error): pass
 class UnimplementedHmacDigestAuthOptionError(HttpLib2Error): pass
+class RelativeURIError(HttpLib2Error): pass
 
 # Open Items:
 # -----------
@@ -125,6 +126,8 @@
 
 def urlnorm(uri):
     (scheme, authority, path, query, fragment) = parse_uri(uri)
+    if not scheme or not authority:
+        raise RelativeURIError("Only absolute URIs are allowed. uri = %s" % uri)
     authority = authority.lower()
     scheme = scheme.lower()
     if not path: 
diff --git a/httplib2test.py b/httplib2test.py
index edda403..33e50d6 100755
--- a/httplib2test.py
+++ b/httplib2test.py
@@ -48,6 +48,11 @@
         self.assertEqual( "http://example.org/mypath?a=b", httplib2.urlnorm("http://EXAMple.org/mypath?a=b")[-1])
         self.assertEqual( "http://localhost:80/", httplib2.urlnorm("http://localhost:80")[-1])
         self.assertEqual( httplib2.urlnorm("http://localhost:80/"), httplib2.urlnorm("HTTP://LOCALHOST:80"))
+        try:
+            httplib2.urlnorm("/")
+            self.fail("Non-absolute URIs should raise an exception")
+        except httplib2.RelativeURIError:
+            pass
 
 class UrlSafenameTest(unittest.TestCase):
     def test(self):