diff --git a/requests/utils.py b/requests/utils.py
index c9746d64..16f7b98f 100644
--- a/requests/utils.py
+++ b/requests/utils.py
@@ -87,8 +87,10 @@ def super_len(o):
             current_position = o.tell()
         except (OSError, IOError):
             # This can happen in some weird situations, such as when the file
-            # is actually a special file descriptor like stdin.
-            current_position = 0
+            # 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
 
     return max(0, total_length - current_position)
 
diff --git a/tests/test_utils.py b/tests/test_utils.py
index afb38315..24b40b96 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -44,7 +44,7 @@ class TestSuperLen:
             def tell(self):
                 raise error()
 
-        assert super_len(BoomFile()) == 5
+        assert super_len(BoomFile()) == 0
 
 
 class TestGetEnvironProxies: