diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index bae432d33b0bd4..b71e210934ef00 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -741,6 +741,9 @@ as internal buffering of data.
    <fd_inheritance>` by default or non-inheritable if *inheritable*
    is ``False``.
 
+   If *fd* is valid and equal to *fd2*, this function has no effect
+   regardless of the value of *inheritable*.
+
    .. versionchanged:: 3.4
       Add the optional *inheritable* parameter.
 
diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index 77e4a008ae61e8..81d58ced068180 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -3102,6 +3102,18 @@ def test_dup2(self):
         self.assertEqual(os.dup2(fd, fd3, inheritable=False), fd3)
         self.assertFalse(os.get_inheritable(fd3))
 
+        # dup2(fd, fd) must have no effect for a valid fd
+        # Issue #26935: Avoid failure due to a bionic bug
+        # in old Android.
+        if (not hasattr(sys, 'getandroidapilevel') or
+                sys.getandroidapilevel() >= 23):
+            os.set_inheritable(fd, True)
+            os.dup2(fd, fd, inheritable=False)
+            self.assertTrue(os.get_inheritable(fd))
+            os.set_inheritable(fd, False)
+            os.dup2(fd, fd, inheritable=True)
+            self.assertFalse(os.get_inheritable(fd))
+
     @unittest.skipUnless(hasattr(os, 'openpty'), "need os.openpty()")
     def test_openpty(self):
         master_fd, slave_fd = os.openpty()
diff --git a/Misc/NEWS.d/next/Library/2018-02-28-12-36-16.bpo-32862.CUwrAr.rst b/Misc/NEWS.d/next/Library/2018-02-28-12-36-16.bpo-32862.CUwrAr.rst
new file mode 100644
index 00000000000000..31b807c5891698
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-02-28-12-36-16.bpo-32862.CUwrAr.rst
@@ -0,0 +1 @@
+Make os.dup2(fd, fd) have no effect apart from validating fd.
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index d242df0b6f3106..ee581edac5d0b9 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -8041,7 +8041,7 @@ os_dup2_impl(PyObject *module, int fd, int fd2, int inheritable)
     res = fd2; // msvcrt dup2 returns 0 on success.
 
     /* Character files like console cannot be make non-inheritable */
-    if (!inheritable && _Py_set_inheritable(fd2, 0, NULL) < 0) {
+    if (!inheritable && fd != fd2 && _Py_set_inheritable(fd2, 0, NULL) < 0) {
         close(fd2);
         return -1;
     }
@@ -8061,7 +8061,7 @@ os_dup2_impl(PyObject *module, int fd, int fd2, int inheritable)
 #else
 
 #ifdef HAVE_DUP3
-    if (!inheritable && dup3_works != 0) {
+    if (!inheritable && fd != fd2 && dup3_works != 0) {
         Py_BEGIN_ALLOW_THREADS
         res = dup3(fd, fd2, O_CLOEXEC);
         Py_END_ALLOW_THREADS
@@ -8075,7 +8075,7 @@ os_dup2_impl(PyObject *module, int fd, int fd2, int inheritable)
         }
     }
 
-    if (inheritable || dup3_works == 0)
+    if (inheritable || fd == fd2 || dup3_works == 0)
     {
 #endif
         Py_BEGIN_ALLOW_THREADS
@@ -8086,7 +8086,8 @@ os_dup2_impl(PyObject *module, int fd, int fd2, int inheritable)
             return -1;
         }
 
-        if (!inheritable && _Py_set_inheritable(fd2, 0, NULL) < 0) {
+        if (!inheritable && fd != fd2 && _Py_set_inheritable(fd2, 0, NULL) < 0)
+        {
             close(fd2);
             return -1;
         }