diff --git a/pre_commit_hooks/requirements_txt_fixer.py b/pre_commit_hooks/requirements_txt_fixer.py
index 4575975..eff7935 100644
--- a/pre_commit_hooks/requirements_txt_fixer.py
+++ b/pre_commit_hooks/requirements_txt_fixer.py
@@ -40,11 +40,16 @@ class Requirement(object):
 
 def fix_requirements(f):  # type: (IO[bytes]) -> int
     requirements = []  # type: List[Requirement]
-    before = tuple(f)
+    before = list(f)
     after = []  # type: List[bytes]
 
     before_string = b''.join(before)
 
+    # adds new line in case one is missing
+    # AND a change to the requirements file is needed regardless:
+    if before and not before[-1].endswith(b'\n'):
+        before[-1] += b'\n'
+
     # If the file is empty (i.e. only whitespace/newlines) exit early
     if before_string.strip() == b'':
         return PASS
diff --git a/tests/requirements_txt_fixer_test.py b/tests/requirements_txt_fixer_test.py
index c7c6e47..2e2eab6 100644
--- a/tests/requirements_txt_fixer_test.py
+++ b/tests/requirements_txt_fixer_test.py
@@ -15,6 +15,9 @@ from pre_commit_hooks.requirements_txt_fixer import Requirement
         (b'foo\n# comment at end\n', PASS, b'foo\n# comment at end\n'),
         (b'foo\nbar\n', FAIL, b'bar\nfoo\n'),
         (b'bar\nfoo\n', PASS, b'bar\nfoo\n'),
+        (b'a\nc\nb\n', FAIL, b'a\nb\nc\n'),
+        (b'a\nc\nb', FAIL, b'a\nb\nc\n'),
+        (b'a\nb\nc', FAIL, b'a\nb\nc\n'),
         (
             b'#comment1\nfoo\n#comment2\nbar\n',
             FAIL,