diff --git a/requests/utils.py b/requests/utils.py
index 149b7a0d..4b2126e6 100644
--- a/requests/utils.py
+++ b/requests/utils.py
@@ -45,7 +45,7 @@ def dict_to_sequence(d):
 
 
 def super_len(o):
-    total_length = 0
+    total_length = None
     current_position = 0
 
     if hasattr(o, '__len__'):
@@ -54,10 +54,6 @@ def super_len(o):
     elif hasattr(o, 'len'):
         total_length = o.len
 
-    elif hasattr(o, 'getvalue'):
-        # e.g. BytesIO, cStringIO.StringIO
-        total_length = len(o.getvalue())
-
     elif hasattr(o, 'fileno'):
         try:
             fileno = o.fileno()
@@ -87,7 +83,22 @@ def super_len(o):
             # is actually a special file descriptor like stdin. In this
             # instance, we don't know what the length is, so set it to zero and
             # let requests chunk it instead.
-            current_position = total_length
+            if total_length is not None:
+                current_position = total_length
+
+        if hasattr(o, 'seek') and total_length is None:
+            # StringIO and BytesIO have seek but no useable fileno
+
+            # seek to end of file
+            o.seek(0, 2)
+            total_length = o.tell()
+
+            # seek back to current position to support
+            # partially read file-like objects
+            o.seek(current_position or 0)
+
+    if total_length is None:
+        total_length = 0
 
     return max(0, total_length - current_position)
 
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 03cff7a6..7e0b4f28 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -66,6 +66,34 @@ class TestSuperLen:
             assert super_len(fd) == 4
         assert len(recwarn) == warnings_num
 
+    def test_super_len_with__len__(self):
+        foo = [1,2,3,4]
+        len_foo = super_len(foo)
+        assert len_foo == 4
+
+    def test_super_len_with_no__len__(self):
+        class LenFile(object):
+            def __init__(self):
+                self.len = 5
+
+        assert super_len(LenFile()) == 5
+
+    def test_super_len_with_tell(self):
+        foo = StringIO.StringIO('12345')
+        assert super_len(foo) == 5
+        foo.read(2)
+        assert super_len(foo) == 3
+
+    def test_super_len_with_fileno(self):
+        with open(__file__, 'rb') as f:
+            length = super_len(f)
+            file_data = f.read()
+        assert length == len(file_data)
+
+    def test_super_len_with_no_matches(self):
+        """Ensure that objects without any length methods default to 0"""
+        assert super_len(object()) == 0
+
 
 class TestToKeyValList: