diff --git a/sphinx/util/build_phase.py b/sphinx/util/build_phase.py
index e5a53551c..48e75675d 100644
--- a/sphinx/util/build_phase.py
+++ b/sphinx/util/build_phase.py
@@ -9,10 +9,7 @@
     :license: BSD, see LICENSE for details.
 """
 
-try:
-    from enum import IntEnum
-except ImportError:  # py27
-    IntEnum = object  # type: ignore
+from enum import IntEnum
 
 
 class BuildPhase(IntEnum):