diff --git a/sphinx/environment.py b/sphinx/environment.py
index 8d0789cfa..9e5a870a4 100644
--- a/sphinx/environment.py
+++ b/sphinx/environment.py
@@ -40,7 +40,7 @@ from sphinx import addnodes
 from sphinx.util import url_re, get_matching_docs, docname_join, split_into, \
     FilenameUniqDict, get_figtype, import_object, split_index_msg
 from sphinx.util.nodes import clean_astext, make_refnode, WarningStream, is_translatable
-from sphinx.util.osutil import SEP, getcwd, fs_encoding
+from sphinx.util.osutil import SEP, getcwd, fs_encoding, ensuredir
 from sphinx.util.i18n import find_catalog_files
 from sphinx.util.console import bold, purple
 from sphinx.util.matching import compile_matchers
@@ -855,9 +855,7 @@ class BuildEnvironment:
         # save the parsed doctree
         doctree_filename = self.doc2path(docname, self.doctreedir,
                                          '.doctree')
-        dirname = path.dirname(doctree_filename)
-        if not path.isdir(dirname):
-            os.makedirs(dirname)
+        ensuredir(path.dirname(doctree_filename))
         f = open(doctree_filename, 'wb')
         try:
             pickle.dump(doctree, f, pickle.HIGHEST_PROTOCOL)