diff --git a/src/base64io/__init__.py b/src/base64io/__init__.py
index e687913..b6a4a78 100644
--- a/src/base64io/__init__.py
+++ b/src/base64io/__init__.py
@@ -43,6 +43,15 @@ def _py2():
     return sys.version_info[0] == 2
 
 
+if not _py2():
+    # The "file" object does not exist in Python 3, but we need to reference
+    # it in Python 2 code paths. Defining this here accomplishes two things:
+    # First, it allows linters to accept "file" as a defined object in Python 3.
+    # Second, it will serve as a canary to ensure that there are no references
+    # to "file" in Python 3 code paths.
+    file = NotImplemented  # pylint: disable=invalid-name
+
+
 class Base64IO(io.IOBase):
     """Base64 stream with context manager support.
 
@@ -121,9 +130,8 @@ class Base64IO(io.IOBase):
         try:
             method = getattr(self.__wrapped, method_name)
         except AttributeError:
-            if _py2() and isinstance(self.__wrapped, file):  # type: ignore # noqa pylint: disable=undefined-variable
-                if mode in self.__wrapped.mode:
-                    return True
+            if _py2() and isinstance(self.__wrapped, file) and mode in self.__wrapped.mode:
+                return True
             return False
         else:
             return method()
@@ -316,9 +324,15 @@ class Base64IO(io.IOBase):
         :rtype: list of bytes
         """
         lines = []
+        total_len = 0
+        hint_defined = hint > 0
+
         for line in self:  # type: ignore
             lines.append(line)
-            if hint > 0 and len(lines) * io.DEFAULT_BUFFER_SIZE > hint:
+            total_len += len(line)
+
+            hint_satisfied = total_len > hint
+            if hint_defined and hint_satisfied:
                 break
         return lines
 
diff --git a/test/unit/test_base64_stream.py b/test/unit/test_base64_stream.py
index b0f114a..de8410c 100644
--- a/test/unit/test_base64_stream.py
+++ b/test/unit/test_base64_stream.py
@@ -10,7 +10,7 @@
 # distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
 # ANY KIND, either express or implied. See the License for the specific
 # language governing permissions and limitations under the License.
-"""Unit test suite for ``aws_encryption_sdk_cli.internal.encoding``."""
+"""Unit test suite for ``base64io.Base64IO``."""
 from __future__ import division
 
 import base64
diff --git a/test/unit/test_base64io.py b/test/unit/test_base64io.py
new file mode 100644
index 0000000..dfb9d20
--- /dev/null
+++ b/test/unit/test_base64io.py
@@ -0,0 +1,39 @@
+# Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"). You
+# may not use this file except in compliance with the License. A copy of
+# the License is located at
+#
+# http://aws.amazon.com/apache2.0/
+#
+# or in the "license" file accompanying this file. This file is
+# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
+# ANY KIND, either express or implied. See the License for the specific
+# language governing permissions and limitations under the License.
+"""Unit test suite for ``base64io`` helpers."""
+import sys
+
+import pytest
+
+import base64io
+
+pytestmark = [pytest.mark.unit]
+
+
+def test_py2():
+    is_python2 = sys.version_info[0] == 2
+
+    assert (is_python2 and base64io._py2()) or (not is_python2 and not base64io._py2())
+
+
+def test_file():
+    is_python2 = sys.version_info[0] == 2
+
+    if is_python2:
+        # If we are in Python 2, the "file" assignment should not
+        # happen because it is a builtin object.
+        assert not hasattr(base64io, 'file')
+    else:
+        # If we are in Python 3, the "file" assignment should happen
+        # to provide a concrete definition of the "file" name.
+        assert base64io.file is NotImplemented