diff --git a/setup.cfg b/setup.cfg
index 1f5bbd1cd..e4d577f93 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -40,6 +40,7 @@ paths =
     .
 
 [mypy]
+python_version = 3.5
 show_column_numbers = True
 show_error_context = True
 ignore_missing_imports = True
diff --git a/sphinx/__init__.py b/sphinx/__init__.py
index 1c8338643..690e0d71f 100644
--- a/sphinx/__init__.py
+++ b/sphinx/__init__.py
@@ -56,8 +56,8 @@ if __version__.endswith('+'):
     __version__ = __version__[:-1]  # remove '+' for PEP-440 version spec.
     try:
         ret = subprocess.run(['git', 'show', '-s', '--pretty=format:%h'],
-                             stdout=PIPE, stderr=PIPE, encoding='ascii')
+                             stdout=PIPE, stderr=PIPE)
         if ret.stdout:
-            __display_version__ += '/' + ret.stdout.strip()
+            __display_version__ += '/' + ret.stdout.decode('ascii').strip()
     except Exception:
         pass