diff --git a/Include/internal/pycore_global_objects_fini_generated.h b/Include/internal/pycore_global_objects_fini_generated.h
index 89ec8cbbbcd649..5e00700cdaa259 100644
--- a/Include/internal/pycore_global_objects_fini_generated.h
+++ b/Include/internal/pycore_global_objects_fini_generated.h
@@ -771,6 +771,7 @@ _PyStaticObjects_CheckRefcnt(PyInterpreterState *interp) {
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(_restype_));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(_showwarnmsg));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(_shutdown));
+    _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(_size));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(_slotnames));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(_strptime_datetime));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(_swappedbytes_));
diff --git a/Include/internal/pycore_global_strings.h b/Include/internal/pycore_global_strings.h
index 62c3ee3ae2a0bd..78ad389c8c4320 100644
--- a/Include/internal/pycore_global_strings.h
+++ b/Include/internal/pycore_global_strings.h
@@ -260,6 +260,7 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(_restype_)
         STRUCT_FOR_ID(_showwarnmsg)
         STRUCT_FOR_ID(_shutdown)
+        STRUCT_FOR_ID(_size)
         STRUCT_FOR_ID(_slotnames)
         STRUCT_FOR_ID(_strptime_datetime)
         STRUCT_FOR_ID(_swappedbytes_)
diff --git a/Include/internal/pycore_runtime_init_generated.h b/Include/internal/pycore_runtime_init_generated.h
index 1defa39f816e78..05d27b40fd543f 100644
--- a/Include/internal/pycore_runtime_init_generated.h
+++ b/Include/internal/pycore_runtime_init_generated.h
@@ -769,6 +769,7 @@ extern "C" {
     INIT_ID(_restype_), \
     INIT_ID(_showwarnmsg), \
     INIT_ID(_shutdown), \
+    INIT_ID(_size), \
     INIT_ID(_slotnames), \
     INIT_ID(_strptime_datetime), \
     INIT_ID(_swappedbytes_), \
diff --git a/Include/internal/pycore_unicodeobject_generated.h b/Include/internal/pycore_unicodeobject_generated.h
index be9baa3eebecfc..b4c1329624e7fd 100644
--- a/Include/internal/pycore_unicodeobject_generated.h
+++ b/Include/internal/pycore_unicodeobject_generated.h
@@ -621,6 +621,9 @@ _PyUnicode_InitStaticStrings(PyInterpreterState *interp) {
     string = &_Py_ID(_shutdown);
     assert(_PyUnicode_CheckConsistency(string, 1));
     _PyUnicode_InternInPlace(interp, &string);
+    string = &_Py_ID(_size);
+    assert(_PyUnicode_CheckConsistency(string, 1));
+    _PyUnicode_InternInPlace(interp, &string);
     string = &_Py_ID(_slotnames);
     assert(_PyUnicode_CheckConsistency(string, 1));
     _PyUnicode_InternInPlace(interp, &string);
diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 32698abac78d25..a4a28a17643f7f 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -238,7 +238,7 @@ def open(file, mode="r", buffering=-1, encoding=None, errors=None,
     result = raw
     try:
         line_buffering = False
-        if buffering == 1 or buffering < 0 and raw.isatty():
+        if buffering == 1 or buffering < 0 and getattr(raw, '_size', 0) == 0 and raw.isatty():
             buffering = -1
             line_buffering = True
         if buffering < 0:
@@ -1571,6 +1571,7 @@ def __init__(self, file, mode='r', closefd=True, opener=None):
             self._blksize = getattr(fdfstat, 'st_blksize', 0)
             if self._blksize <= 1:
                 self._blksize = DEFAULT_BUFFER_SIZE
+            self._size = fdfstat.st_size
 
             if _setmode:
                 # don't translate newlines (\r\n <=> \n)
diff --git a/Modules/_io/_iomodule.c b/Modules/_io/_iomodule.c
index 173f5b55e5f732..8cf501fa383d64 100644
--- a/Modules/_io/_iomodule.c
+++ b/Modules/_io/_iomodule.c
@@ -209,6 +209,7 @@ _io_open_impl(PyObject *module, PyObject *file, const char *mode,
 
     char rawmode[6], *m;
     int line_buffering, is_number, isatty = 0;
+    __int64_t size = 0;
 
     PyObject *raw, *modeobj = NULL, *buffer, *wrapper, *result = NULL, *path_or_fd = NULL;
 
@@ -346,6 +347,16 @@ _io_open_impl(PyObject *module, PyObject *file, const char *mode,
 
     /* buffering */
     if (buffering < 0) {
+        PyObject *size_obj;
+        size_obj = PyObject_GetAttr(raw, &_Py_ID(_size));
+        if (size_obj == NULL)
+            goto error;
+        size = PyLong_AsLongLong(size_obj);
+        Py_DECREF(size_obj);
+        if (size == -1 && PyErr_Occurred())
+            goto error;
+    }
+    if (buffering < 0 && size == 0) {
         PyObject *res = PyObject_CallMethodNoArgs(raw, &_Py_ID(isatty));
         if (res == NULL)
             goto error;
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index 8a73ea0365b7a3..f3f0bf147124ed 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -72,6 +72,7 @@ typedef struct {
     unsigned int closefd : 1;
     char finalizing;
     unsigned int blksize;
+    __int64_t size;
     PyObject *weakreflist;
     PyObject *dict;
 } fileio;
@@ -196,6 +197,7 @@ fileio_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
         self->appending = 0;
         self->seekable = -1;
         self->blksize = 0;
+        self->size = 0;
         self->closefd = 1;
         self->weakreflist = NULL;
     }
@@ -475,6 +477,7 @@ _io_FileIO___init___impl(fileio *self, PyObject *nameobj, const char *mode,
         if (fdfstat.st_blksize > 1)
             self->blksize = fdfstat.st_blksize;
 #endif /* HAVE_STRUCT_STAT_ST_BLKSIZE */
+	self->size = fdfstat.st_size;
     }
 
 #if defined(MS_WINDOWS) || defined(__CYGWIN__)
@@ -1205,6 +1208,7 @@ static PyGetSetDef fileio_getsetlist[] = {
 
 static PyMemberDef fileio_members[] = {
     {"_blksize", Py_T_UINT, offsetof(fileio, blksize), 0},
+    {"_size", T_UINT, offsetof(fileio, size), 0},
     {"_finalizing", Py_T_BOOL, offsetof(fileio, finalizing), 0},
     {"__weaklistoffset__", Py_T_PYSSIZET, offsetof(fileio, weakreflist), Py_READONLY},
     {"__dictoffset__", Py_T_PYSSIZET, offsetof(fileio, dict), Py_READONLY},