diff --git a/sphinx/ext/intersphinx.py b/sphinx/ext/intersphinx.py
index 16a487ef8..5e035ece1 100644
--- a/sphinx/ext/intersphinx.py
+++ b/sphinx/ext/intersphinx.py
@@ -125,6 +125,14 @@ def read_inventory_v2(f, uri, join, bufsize=16*1024):
     return invdata
 
 
+def read_inventory(f, uri, join, bufsize=16*1024):
+    line = f.readline().rstrip().decode('utf-8')
+    if line == '# Sphinx inventory version 1':
+        return read_inventory_v1(f, uri, join)
+    elif line == '# Sphinx inventory version 2':
+        return read_inventory_v2(f, uri, join, bufsize=bufsize)
+
+
 def _strip_basic_auth(url):
     """Returns *url* with basic auth credentials removed. Also returns the
     basic auth username and password if they're present in *url*.
@@ -227,7 +235,6 @@ def fetch_inventory(app, uri, inv):
     if not localuri:
         # case: inv URI points to remote resource; strip any existing auth
         uri, _, _ = _strip_basic_auth(uri)
-    join = localuri and path.join or posixpath.join
     try:
         if '://' in inv:
             f = _read_from_url(inv)
@@ -245,18 +252,12 @@ def fetch_inventory(app, uri, inv):
 
                 if uri in (inv, path.dirname(inv), path.dirname(inv) + '/'):
                     uri = path.dirname(newinv)
-        line = f.readline().rstrip().decode('utf-8')
-        try:
-            if line == '# Sphinx inventory version 1':
-                invdata = read_inventory_v1(f, uri, join)
-            elif line == '# Sphinx inventory version 2':
-                invdata = read_inventory_v2(f, uri, join)
-            else:
-                raise ValueError
-            f.close()
-        except ValueError:
-            f.close()
-            raise ValueError('unknown or unsupported inventory version')
+        with f:
+            try:
+                join = localuri and path.join or posixpath.join
+                invdata = read_inventory(f, uri, join)
+            except ValueError:
+                raise ValueError('unknown or unsupported inventory version')
     except Exception as err:
         app.warn('intersphinx inventory %r not readable due to '
                  '%s: %s' % (inv, err.__class__.__name__, err))
diff --git a/tests/test_ext_intersphinx.py b/tests/test_ext_intersphinx.py
index 334d53971..ebbf76fca 100644
--- a/tests/test_ext_intersphinx.py
+++ b/tests/test_ext_intersphinx.py
@@ -17,7 +17,7 @@ from six import BytesIO
 from docutils import nodes
 
 from sphinx import addnodes
-from sphinx.ext.intersphinx import read_inventory_v1, read_inventory_v2, \
+from sphinx.ext.intersphinx import read_inventory, \
     load_mappings, missing_reference, _strip_basic_auth, _read_from_url, \
     _get_safe_url, fetch_inventory, INVENTORY_FILENAME
 
@@ -49,8 +49,7 @@ a term including:colon std:term -1 glossary.html#term-a-term-including-colon -
 
 def test_read_inventory_v1():
     f = BytesIO(inventory_v1)
-    f.readline()
-    invdata = read_inventory_v1(f, '/util', posixpath.join)
+    invdata = read_inventory(f, '/util', posixpath.join)
     assert invdata['py:module']['module'] == \
         ('foo', '1.0', '/util/foo.html#module-module', '-')
     assert invdata['py:class']['module.cls'] == \
@@ -59,13 +58,11 @@ def test_read_inventory_v1():
 
 def test_read_inventory_v2():
     f = BytesIO(inventory_v2)
-    f.readline()
-    invdata1 = read_inventory_v2(f, '/util', posixpath.join)
+    invdata1 = read_inventory(f, '/util', posixpath.join)
 
     # try again with a small buffer size to test the chunking algorithm
     f = BytesIO(inventory_v2)
-    f.readline()
-    invdata2 = read_inventory_v2(f, '/util', posixpath.join, bufsize=5)
+    invdata2 = read_inventory(f, '/util', posixpath.join, bufsize=5)
 
     assert invdata1 == invdata2