diff --git a/sphinx/config.py b/sphinx/config.py
index 441da2fee..25450c156 100644
--- a/sphinx/config.py
+++ b/sphinx/config.py
@@ -22,6 +22,7 @@ from sphinx.util.pycompat import execfile_, NoneType
 from sphinx.util.i18n import format_date
 
 nonascii_re = re.compile(br'[\x80-\xff]')
+copyright_year_re = re.compile(br'^((\d{4}-)?)(\d{4})(?=[ ,])')
 
 CONFIG_SYNTAX_ERROR = "There is a syntax error in your configuration file: %s"
 if PY3:
@@ -302,11 +303,10 @@ class Config(object):
         # correct values of copyright year that are not coherent with
         # the SOURCE_DATE_EPOCH environment variable:
         if getenv('SOURCE_DATE_EPOCH') is not None:
-            for k in ['copyright','epub_copyright']:
+            for k in ('copyright','epub_copyright'):
                 if k in config:
-                    config[k] = re.sub('^((\d{4}-)?)(\d{4})(?=[ ,])',
-                                       '\g<1>%s' % format_date('%Y'),
-                                       config[k])
+                    config[k] = copyright_year_re.sub('\g<1>%s' % format_date('%Y'),
+                                                      config[k])
 
     def check_types(self, warn):
         # check all values for deviation from the default value's type, since
diff --git a/tests/test_correct_year.py b/tests/test_correct_year.py
index e09c3b630..7a156cbf2 100644
--- a/tests/test_correct_year.py
+++ b/tests/test_correct_year.py
@@ -14,34 +14,36 @@ from util import TestApp
 
 
 def test_correct_year():
-    # save current value of SOURCE_DATE_EPOCH
-    sde = os.environ.pop('SOURCE_DATE_EPOCH',None)
+    try:
+        # save current value of SOURCE_DATE_EPOCH
+        sde = os.environ.pop('SOURCE_DATE_EPOCH',None)
 
-    # test with SOURCE_DATE_EPOCH unset: no modification
-    app = TestApp(buildername='html',testroot='correct-year')
-    app.builder.build_all()
-    content = (app.outdir / 'contents.html').text()
-    app.cleanup()
-    assert '2006-2009' in content
+        # test with SOURCE_DATE_EPOCH unset: no modification
+        app = TestApp(buildername='html',testroot='correct-year')
+        app.builder.build_all()
+        content = (app.outdir / 'contents.html').text()
+        app.cleanup()
+        assert '2006-2009' in content
 
-    # test with SOURCE_DATE_EPOCH set: copyright year should be
-    # updated
-    os.environ['SOURCE_DATE_EPOCH'] = "1293840000"
-    app = TestApp(buildername='html',testroot='correct-year')
-    app.builder.build_all()
-    content = (app.outdir / 'contents.html').text()
-    app.cleanup()
-    assert '2006-2011' in content
+        # test with SOURCE_DATE_EPOCH set: copyright year should be
+        # updated
+        os.environ['SOURCE_DATE_EPOCH'] = "1293840000"
+        app = TestApp(buildername='html',testroot='correct-year')
+        app.builder.build_all()
+        content = (app.outdir / 'contents.html').text()
+        app.cleanup()
+        assert '2006-2011' in content
 
-    os.environ['SOURCE_DATE_EPOCH'] = "1293839999"
-    app = TestApp(buildername='html',testroot='correct-year')
-    app.builder.build_all()
-    content = (app.outdir / 'contents.html').text()
-    app.cleanup()
-    assert '2006-2010' in content
+        os.environ['SOURCE_DATE_EPOCH'] = "1293839999"
+        app = TestApp(buildername='html',testroot='correct-year')
+        app.builder.build_all()
+        content = (app.outdir / 'contents.html').text()
+        app.cleanup()
+        assert '2006-2010' in content
 
-    # Restores SOURCE_DATE_EPOCH
-    if sde == None:
-        os.environ.pop('SOURCE_DATE_EPOCH',None)
-    else:
-        os.environ['SOURCE_DATE_EPOCH'] = sde
+    finally:
+        # Restores SOURCE_DATE_EPOCH
+        if sde == None:
+            os.environ.pop('SOURCE_DATE_EPOCH',None)
+        else:
+            os.environ['SOURCE_DATE_EPOCH'] = sde