diff --git a/README.md b/README.md
index d46f93f..968c098 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,7 @@ exceptions:
 - Multi-line docstrings: The first line of text (summary line) appears on the same line as the opening three double-quotes.
 -  Base Class Inheritance
 	- If a class or nested class inherits from no other base classes, explicitly inherit from object.
-	- This won't be enforced for our pure Python 3 code, but we will enforce for Python 2 and 2/3 compatbile code.
+	- This won't be enforced for our pure Python 3 code, but we will enforce for Python 2 and 2/3 compatible code.
 - Variable/module-name collisions: Variable names may be suffixed with an underscore to avoid collisions with imported modules (an extension of the [PEP-8 convention](https://www.python.org/dev/peps/pep-0008/#descriptive-naming-styles) for collisions with builtins).
 
 
@@ -29,7 +29,7 @@ exceptions:
 Projects that are producing libraries to be used in other projects should choose their release version numbers using [Semantic Versioning 2.0.0](http://semver.org/spec/v2.0.0.html), i.e.
 
 > Given a version number MAJOR.MINOR.PATCH, increment the:
-> 
+>
 > MAJOR version when you make incompatible API changes,
 > MINOR version when you add functionality in a backwards-compatible manner, and
 > PATCH version when you make backwards-compatible bug fixes.
diff --git a/shopify_python/git_utils.py b/shopify_python/git_utils.py
index e7e24ed..39ee3c2 100644
--- a/shopify_python/git_utils.py
+++ b/shopify_python/git_utils.py
@@ -13,12 +13,12 @@ class GitUtilsException(Exception):
     pass
 
 
-def _remote_origin_master(git_repo):
-    # type: (repo.Repo) -> head.Head
-    remote_master = git_repo.heads.master.tracking_branch()
-    if not remote_master or not remote_master.is_valid():
-        raise GitUtilsException("Unable to locate remote branch origin/master")
-    return remote_master
+def _remote_origin_branch(git_repo, branch):
+    # type: (repo.Repo, str) -> head.Head
+    remote_branch = git_repo.heads[branch].tracking_branch()
+    if not remote_branch or not remote_branch.is_valid():
+        raise GitUtilsException("Unable to locate remote branch origin/{}".format(branch))
+    return remote_branch
 
 
 def _modified_in_branch(git_repo, other_ref):
@@ -48,12 +48,12 @@ def _file_is_python(path):
         return False
 
 
-def changed_python_files_in_tree(root_path):
-    # type: (str) -> typing.List[str]
+def changed_python_files_in_tree(root_path, base='master'):
+    # type: (str, typing.Optional[str]) -> typing.List[str]
 
     git_repo = repo.Repo(root_path)
-    remote_master = _remote_origin_master(git_repo)
-    modified = _modified_in_branch(git_repo, remote_master)
+    remote_branch = _remote_origin_branch(git_repo, base)
+    modified = _modified_in_branch(git_repo, remote_branch)
     abs_modified = [os.path.join(git_repo.working_dir, x) for x in modified]
     return [mod for (mod, abs_mod) in zip(modified, abs_modified)
             if os.path.exists(abs_mod) and os.path.isfile(abs_mod) and _file_is_python(abs_mod)]
diff --git a/tests/shopify_python/test_git_utils.py b/tests/shopify_python/test_git_utils.py
index 3dab39f..9d0435d 100644
--- a/tests/shopify_python/test_git_utils.py
+++ b/tests/shopify_python/test_git_utils.py
@@ -79,8 +79,8 @@ def test_detects_changed_python_files(main_repo, python_file, python_script):
     main_repo.create_head('foo').checkout()
     main_repo.index.add([python_file, python_script])
     main_repo.index.commit("adding python files")
-
     changed_files = git_utils.changed_python_files_in_tree(main_repo.working_dir)
+
     assert sorted(changed_files) == [
         os.path.basename(python_script),
         os.path.basename(python_file),