diff -r cca2ed4e8b41 Lib/test/test_coroutines.py
--- a/Lib/test/test_coroutines.py	Thu Dec 17 10:35:05 2015 +0000
+++ b/Lib/test/test_coroutines.py	Thu Dec 17 13:10:29 2015 -0500
@@ -569,6 +569,97 @@
                                     "coroutine ignored GeneratorExit"):
             c.close()
 
+    def test_func_15(self):
+        # See http://bugs.python.org/issue25887 for details
+
+        async def send():
+            return 'spam'
+        async def reader(coro):
+            return await coro
+
+        spammer = send()
+
+        with self.assertRaisesRegex(StopIteration, 'spam'):
+            reader(spammer).send(None)
+
+        with self.assertRaisesRegex(RuntimeError,
+                                    'coroutine was already awaited'):
+            reader(spammer).send(None)
+
+    def test_func_16(self):
+        # See http://bugs.python.org/issue25887 for details
+
+        @types.coroutine
+        def nop():
+            yield
+        async def send():
+            await nop()
+            return 'spam'
+        async def read(coro):
+            await nop()
+            return await coro
+
+        spammer = send()
+
+        reader = read(spammer)
+        reader.send(None)
+        reader.send(None)
+        with self.assertRaisesRegex(Exception, 'ham'):
+            reader.throw(Exception('ham'))
+
+        reader = read(spammer)
+        reader.send(None)
+        with self.assertRaisesRegex(RuntimeError,
+                                    'coroutine was already awaited'):
+            reader.send(None)
+
+        with self.assertRaisesRegex(RuntimeError,
+                                    'coroutine was already awaited'):
+            reader.throw(Exception('wat'))
+
+    def test_func_17(self):
+        # See http://bugs.python.org/issue25887 for details
+
+        async def coroutine():
+            return 'spam'
+
+        coro = coroutine()
+        with self.assertRaisesRegex(StopIteration, 'spam'):
+            coro.send(None)
+
+        with self.assertRaisesRegex(RuntimeError,
+                                    'coroutine was already awaited'):
+            coro.send(None)
+
+        with self.assertRaisesRegex(RuntimeError,
+                                    'coroutine was already awaited'):
+            coro.throw(Exception('wat'))
+
+    def test_func_18(self):
+        # See http://bugs.python.org/issue25887 for details
+
+        async def coroutine():
+            return 'spam'
+
+        coro = coroutine()
+        awaitable = coro.__await__()
+        it = iter(awaitable)
+
+        with self.assertRaisesRegex(StopIteration, 'spam'):
+            it.send(None)
+
+        with self.assertRaisesRegex(RuntimeError,
+                                    'coroutine was already awaited'):
+            it.send(None)
+
+        with self.assertRaisesRegex(RuntimeError,
+                                    'coroutine was already awaited'):
+            next(it)
+
+        with self.assertRaisesRegex(RuntimeError,
+                                    'coroutine was already awaited'):
+            it.throw(Exception('wat'))
+
     def test_cr_await(self):
         @types.coroutine
         def a():
diff -r cca2ed4e8b41 Objects/genobject.c
--- a/Objects/genobject.c	Thu Dec 17 10:35:05 2015 +0000
+++ b/Objects/genobject.c	Thu Dec 17 13:10:29 2015 -0500
@@ -92,9 +92,16 @@
         return NULL;
     }
     if (f == NULL || f->f_stacktop == NULL) {
-        /* Only set exception if called from send() */
-        if (arg && !exc)
+        if (PyCoro_CheckExact(gen)) {
+            /* `gen` is an exhausted coroutine: always raise an error. */
+            PyErr_SetString(
+                PyExc_RuntimeError,
+                "coroutine was already awaited");
+        } else if (arg && !exc) {
+            /* `gen` is an exhausted generator:
+               only set exception if called from send(). */
             PyErr_SetNone(PyExc_StopIteration);
+        }
         return NULL;
     }