diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index b04d23a0c2f..d4cfb6e1264 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -200,38 +200,45 @@ def open(file, mode="r", buffering=-1, encoding=None, errors=None,
                  (appending and "a" or "") +
                  (updating and "+" or ""),
                  closefd, opener=opener)
-    line_buffering = False
-    if buffering == 1 or buffering < 0 and raw.isatty():
-        buffering = -1
-        line_buffering = True
-    if buffering < 0:
-        buffering = DEFAULT_BUFFER_SIZE
-        try:
-            bs = os.fstat(raw.fileno()).st_blksize
-        except (OSError, AttributeError):
-            pass
+    result = raw
+    try:
+        line_buffering = False
+        if buffering == 1 or buffering < 0 and raw.isatty():
+            buffering = -1
+            line_buffering = True
+        if buffering < 0:
+            buffering = DEFAULT_BUFFER_SIZE
+            try:
+                bs = os.fstat(raw.fileno()).st_blksize
+            except (OSError, AttributeError):
+                pass
+            else:
+                if bs > 1:
+                    buffering = bs
+        if buffering < 0:
+            raise ValueError("invalid buffering size")
+        if buffering == 0:
+            if binary:
+                return result
+            raise ValueError("can't have unbuffered text I/O")
+        if updating:
+            buffer = BufferedRandom(raw, buffering)
+        elif creating or writing or appending:
+            buffer = BufferedWriter(raw, buffering)
+        elif reading:
+            buffer = BufferedReader(raw, buffering)
         else:
-            if bs > 1:
-                buffering = bs
-    if buffering < 0:
-        raise ValueError("invalid buffering size")
-    if buffering == 0:
+            raise ValueError("unknown mode: %r" % mode)
+        result = buffer
         if binary:
-            return raw
-        raise ValueError("can't have unbuffered text I/O")
-    if updating:
-        buffer = BufferedRandom(raw, buffering)
-    elif creating or writing or appending:
-        buffer = BufferedWriter(raw, buffering)
-    elif reading:
-        buffer = BufferedReader(raw, buffering)
-    else:
-        raise ValueError("unknown mode: %r" % mode)
-    if binary:
-        return buffer
-    text = TextIOWrapper(buffer, encoding, errors, newline, line_buffering)
-    text.mode = mode
-    return text
+            return result
+        text = TextIOWrapper(buffer, encoding, errors, newline, line_buffering)
+        result = text
+        text.mode = mode
+        return result
+    except:
+        result.close()
+        raise
 
 
 class DocDescriptor:
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 3c2c1025d0c..eef100f7eaf 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -653,6 +653,20 @@ class IOTest(unittest.TestCase):
             fileio.close()
             f2.readline()
 
+    def test_nonbuffered_textio(self):
+        with warnings.catch_warnings(record=True) as recorded:
+            with self.assertRaises(ValueError):
+                self.open(support.TESTFN, 'w', buffering=0)
+            support.gc_collect()
+        self.assertEqual(recorded, [])
+
+    def test_invalid_newline(self):
+        with warnings.catch_warnings(record=True) as recorded:
+            with self.assertRaises(ValueError):
+                self.open(support.TESTFN, 'w', newline='invalid')
+            support.gc_collect()
+        self.assertEqual(recorded, [])
+
 
 class CIOTest(IOTest):
 
diff --git a/Misc/NEWS b/Misc/NEWS
index 99507251149..28474bb626f 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -92,6 +92,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #21310: Fixed possible resource leak in failed open().
+
 - Issue #21256: Printout of keyword args should be in deterministic order in
   a mock function call. This will help to write better doctests.
 
diff --git a/Modules/_io/_iomodule.c b/Modules/_io/_iomodule.c
index be0464c4fa3..1dbd563e2c6 100644
--- a/Modules/_io/_iomodule.c
+++ b/Modules/_io/_iomodule.c
@@ -235,11 +235,12 @@ io_open(PyObject *self, PyObject *args, PyObject *kwds)
     char rawmode[6], *m;
     int line_buffering, isatty;
 
-    PyObject *raw, *modeobj = NULL, *buffer = NULL, *wrapper = NULL;
+    PyObject *raw, *modeobj = NULL, *buffer, *wrapper, *result = NULL;
 
     _Py_IDENTIFIER(isatty);
     _Py_IDENTIFIER(fileno);
     _Py_IDENTIFIER(mode);
+    _Py_IDENTIFIER(close);
 
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|sizzziO:open", kwlist,
                                      &file, &mode, &buffering,
@@ -354,6 +355,7 @@ io_open(PyObject *self, PyObject *args, PyObject *kwds)
                                 "OsiO", file, rawmode, closefd, opener);
     if (raw == NULL)
         return NULL;
+    result = raw;
 
     modeobj = PyUnicode_FromString(mode);
     if (modeobj == NULL)
@@ -412,7 +414,7 @@ io_open(PyObject *self, PyObject *args, PyObject *kwds)
         }
 
         Py_DECREF(modeobj);
-        return raw;
+        return result;
     }
 
     /* wraps into a buffered file */
@@ -433,15 +435,16 @@ io_open(PyObject *self, PyObject *args, PyObject *kwds)
 
         buffer = PyObject_CallFunction(Buffered_class, "Oi", raw, buffering);
     }
-    Py_CLEAR(raw);
     if (buffer == NULL)
         goto error;
+    result = buffer;
+    Py_DECREF(raw);
 
 
     /* if binary, returns the buffered file */
     if (binary) {
         Py_DECREF(modeobj);
-        return buffer;
+        return result;
     }
 
     /* wraps into a TextIOWrapper */
@@ -450,20 +453,35 @@ io_open(PyObject *self, PyObject *args, PyObject *kwds)
 				    buffer,
 				    encoding, errors, newline,
 				    line_buffering);
-    Py_CLEAR(buffer);
     if (wrapper == NULL)
         goto error;
+    result = wrapper;
+    Py_DECREF(buffer);
 
     if (_PyObject_SetAttrId(wrapper, &PyId_mode, modeobj) < 0)
         goto error;
     Py_DECREF(modeobj);
-    return wrapper;
+    return result;
 
   error:
-    Py_XDECREF(raw);
+    if (result != NULL) {
+        PyObject *exc, *val, *tb;
+        PyErr_Fetch(&exc, &val, &tb);
+        if (_PyObject_CallMethodId(result, &PyId_close, NULL) != NULL)
+            PyErr_Restore(exc, val, tb);
+        else {
+            PyObject *val2;
+            PyErr_NormalizeException(&exc, &val, &tb);
+            Py_XDECREF(exc);
+            Py_XDECREF(tb);
+            PyErr_Fetch(&exc, &val2, &tb);
+            PyErr_NormalizeException(&exc, &val2, &tb);
+            PyException_SetContext(val2, val);
+            PyErr_Restore(exc, val2, tb);
+        }
+        Py_DECREF(result);
+    }
     Py_XDECREF(modeobj);
-    Py_XDECREF(buffer);
-    Py_XDECREF(wrapper);
     return NULL;
 }