diff --git a/python/helpers/python-skeletons/os/__init__.py b/python/helpers/python-skeletons/os/__init__.py
index 3d8867d67d98..693818ce40e1 100644
--- a/python/helpers/python-skeletons/os/__init__.py
+++ b/python/helpers/python-skeletons/os/__init__.py
@@ -2,6 +2,9 @@
 
 
 from __future__ import unicode_literals
+import io
+import os
+import subprocess
 import sys
 
 
@@ -311,11 +314,44 @@ def popen(command, mode='r', bufsize=-1):
     :type command: string
     :type mode: string
     :type bufsize: int
-    :rtype: io.FileIO[bytes]
+    :rtype: os._wrap_close
     """
     pass
 
 
+class _wrap_close:
+    def __init__(self, stream, proc):
+        """
+        :type stream: io.TextIOWrapper[unicode]
+        :type proc: subprocess.Popen
+        """
+        pass
+
+    def close(self):
+        """
+        :rtype: int | None
+        """
+        pass
+
+    def __enter__(self):
+        """
+        :rtype: os._wrap_close
+        """
+        pass
+
+    def __exit__(self, *args):
+        pass
+
+    def __getattr__(self, name):
+        pass
+
+    def __iter__(self):
+        """
+        :rtype: collections.Iterator[unicode]
+        """
+        pass
+
+
 def tmpfile():
     """Return a new file object opened in update mode (w+b).
 
diff --git a/python/testData/inspections/PyNoneFunctionAssignmentInspection/OsPopenClose/a.py b/python/testData/inspections/PyNoneFunctionAssignmentInspection/OsPopenClose/a.py
new file mode 100644
index 000000000000..d46a5cac74a6
--- /dev/null
+++ b/python/testData/inspections/PyNoneFunctionAssignmentInspection/OsPopenClose/a.py
@@ -0,0 +1,2 @@
+from os import popen
+ret = popen("non-existent-command").close()
\ No newline at end of file
diff --git a/python/testData/inspections/PyNoneFunctionAssignmentInspection/OsPopenClose/os.py b/python/testData/inspections/PyNoneFunctionAssignmentInspection/OsPopenClose/os.py
new file mode 100644
index 000000000000..be3e93c6ac47
--- /dev/null
+++ b/python/testData/inspections/PyNoneFunctionAssignmentInspection/OsPopenClose/os.py
@@ -0,0 +1,6 @@
+def popen(command, mode='r', bufsize=-1):
+    pass
+
+class _wrap_close:
+    def close(self):
+        pass
\ No newline at end of file
diff --git a/python/testSrc/com/jetbrains/python/inspections/Py3NoneFunctionAssignmentInspectionTest.java b/python/testSrc/com/jetbrains/python/inspections/Py3NoneFunctionAssignmentInspectionTest.java
new file mode 100644
index 000000000000..933729ffdb18
--- /dev/null
+++ b/python/testSrc/com/jetbrains/python/inspections/Py3NoneFunctionAssignmentInspectionTest.java
@@ -0,0 +1,41 @@
+/*
+ * Copyright 2000-2016 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.jetbrains.python.inspections;
+
+import com.intellij.testFramework.LightProjectDescriptor;
+import com.jetbrains.python.fixtures.PyTestCase;
+import org.jetbrains.annotations.Nullable;
+
+public class Py3NoneFunctionAssignmentInspectionTest extends PyTestCase {
+
+  @Nullable
+  @Override
+  protected LightProjectDescriptor getProjectDescriptor() {
+    return ourPy3Descriptor;
+  }
+
+  // PY-21040
+  public void testOsPopenClose() {
+    doMultiFileTest();
+  }
+
+  private void doMultiFileTest() {
+    myFixture.copyDirectoryToProject("inspections/PyNoneFunctionAssignmentInspection/" + getTestName(false) + "/", "");
+    myFixture.configureByFile("a.py");
+    myFixture.enableInspections(PyNoneFunctionAssignmentInspection.class);
+    myFixture.checkHighlighting(false, false, true);
+  }
+}