diff --git a/python/mozbuild/mozbuild/util.py b/python/mozbuild/mozbuild/util.py
index 9917d31fb6f5..19812f4055e1 100644
--- a/python/mozbuild/mozbuild/util.py
+++ b/python/mozbuild/mozbuild/util.py
@@ -1414,22 +1414,6 @@ def ensure_unicode(value, encoding="utf-8"):
     return value
 
 
-def ensure_subprocess_env(env, encoding="utf-8"):
-    """Ensure the environment is in the correct format for the `subprocess`
-    module.
-
-    This will convert all keys and values to bytes on Python 2, and text on
-    Python 3.
-
-    Args:
-        env (dict): Environment to ensure.
-        encoding (str): Encoding to use when converting to/from bytes/text
-                        (default: utf-8).
-    """
-    ensure = ensure_bytes if sys.version_info[0] < 3 else ensure_unicode
-    return {ensure(k, encoding): ensure(v, encoding) for k, v in six.iteritems(env)}
-
-
 def process_time():
     if six.PY2:
         return time.clock()