diff --git a/Doc/c-api/object.rst b/Doc/c-api/object.rst
index d0d45ad..88ba5ac 100644
--- a/Doc/c-api/object.rst
+++ b/Doc/c-api/object.rst
@@ -6,6 +6,19 @@
 ===============
 
 
+.. c:var:: PyObject* Py_NotImplemented
+
+   The ``NotImplemented`` singleton, used to signal that an operation is
+   not implemented for the given type combination.
+
+
+.. c:macro:: Py_RETURN_NOTIMPLEMENTED
+
+   Properly handle returning :c:data:`Py_NotImplemented` from within a C
+   function (that is, increment the reference count of NotImplemented and
+   return it).
+
+
 .. c:function:: int PyObject_Print(PyObject *o, FILE *fp, int flags)
 
    Print an object *o*, on file *fp*.  Returns ``-1`` on error.  The flags argument
diff --git a/Lib/test/pickletester.py b/Lib/test/pickletester.py
index 45e8f74..f90d348 100644
--- a/Lib/test/pickletester.py
+++ b/Lib/test/pickletester.py
@@ -1438,6 +1438,19 @@
     def test_multiple_unpicklings_unseekable(self):
         self._check_multiple_unpicklings(UnseekableIO)
 
+    def test_unpickling_buffering_readline(self):
+        # Issue #12687: the unpickler's buffering logic could fail with
+        # text mode opcodes.
+        data = list(range(10))
+        for proto in protocols:
+            for buf_size in range(1, 11):
+                f = io.BufferedRandom(io.BytesIO(), buffer_size=buf_size)
+                pickler = self.pickler_class(f, protocol=proto)
+                pickler.dump(data)
+                f.seek(0)
+                unpickler = self.unpickler_class(f)
+                self.assertEqual(unpickler.load(), data)
+
 
 if __name__ == "__main__":
     # Print some stuff that can be used to rewrite DATA{0,1,2}
diff --git a/Misc/NEWS b/Misc/NEWS
index 109b4a4..34aac79 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -251,6 +251,9 @@
 Library
 -------
 
+- Issue #12687: Fix a possible buffering bug when unpickling text mode
+  (protocol 0, mostly) pickles.
+
 - Issue #10087: Fix the html output format of the calendar module.
 
 - Issue #12540: Prevent zombie IDLE processes on Windows due to changes
diff --git a/Modules/_pickle.c b/Modules/_pickle.c
index 06bce1e..f147e3e 100644
--- a/Modules/_pickle.c
+++ b/Modules/_pickle.c
@@ -1034,9 +1034,8 @@
         num_read = _Unpickler_ReadFromFile(self, READ_WHOLE_LINE);
         if (num_read < 0)
             return -1;
-        *result = self->input_buffer;
         self->next_read_idx = num_read;
-        return num_read;
+        return _Unpickler_CopyLine(self, self->input_buffer, num_read, result);
     }
  
     /* If we get here, we've run off the end of the input string. Return the