diff --git a/tests/test_io_error_mapping.py b/tests/test_io_error_mapping.py
new file mode 100644
index 0000000..2932d1d
--- /dev/null
+++ b/tests/test_io_error_mapping.py
@@ -0,0 +1,89 @@
+# -*- coding: utf-8 -*-
+#
+# test_io_error_mapping.py
+#
+# Copyright (C) 2006-2020 wolfSSL Inc.
+#
+# This file is part of wolfSSL. (formerly known as CyaSSL)
+#
+# wolfSSL is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# wolfSSL is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
+
+# pylint: disable=missing-docstring, invalid-name, import-error
+# pylint: disable=protected-access
+
+"""
+These tests exercise the error-code-to-exception mapping in SSLSocket's
+read/write/recv_into. wolfSSL_write can return WANT_READ and wolfSSL_read can
+return WANT_WRITE during a renegotiation; non-blocking callers rely on these
+being surfaced as SSLWantReadError / SSLWantWriteError (matching the stdlib
+ssl module) rather than a generic SSLError.
+
+The renegotiation conditions are awkward to force over a real socket, so the
+native wolfSSL_read/wolfSSL_write/wolfSSL_get_error functions are stubbed to
+return the relevant codes and the Python-level mapping is verified directly.
+"""
+
+from types import SimpleNamespace
+
+import pytest
+import wolfssl
+
+
+class _FakeLib:
+    """Stand-in for wolfssl._lib that forces a given I/O return / error."""
+
+    def __init__(self, io_ret, err):
+        self._io_ret = io_ret
+        self._err = err
+
+    def wolfSSL_write(self, ssl, data, length):
+        return self._io_ret
+
+    def wolfSSL_read(self, ssl, data, length):
+        return self._io_ret
+
+    def wolfSSL_get_error(self, ssl, ret):
+        return self._err
+
+
+def _make_socket():
+    """A minimal, non-DTLS SSLSocket that skips __init__/native setup."""
+    sock = wolfssl.SSLSocket.__new__(wolfssl.SSLSocket)
+    sock.native_object = object()      # non-NULL so _check_closed passes
+    sock._connected = True             # so _check_connected is a no-op
+    sock._context = SimpleNamespace(protocol=wolfssl.PROTOCOL_TLS)
+    # The dummy native_object isn't a real cdata pointer, so make __del__
+    # a no-op to avoid wolfSSL_free() choking on it during GC.
+    sock._release_native_object = lambda: None
+    return sock
+
+
+def _patch_lib(monkeypatch, io_ret, err):
+    monkeypatch.setattr(wolfssl, "_lib", _FakeLib(io_ret, err))
+
+
+def test_write_want_read_raises_wantread(monkeypatch):
+    """F-3905: wolfSSL_write returning WANT_READ -> SSLWantReadError."""
+    _patch_lib(monkeypatch, -1, wolfssl._SSL_ERROR_WANT_READ)
+    sock = _make_socket()
+    with pytest.raises(wolfssl.SSLWantReadError):
+        sock.write(b"data")
+
+
+def test_write_want_write_still_raises_wantwrite(monkeypatch):
+    _patch_lib(monkeypatch, -1, wolfssl._SSL_ERROR_WANT_WRITE)
+    sock = _make_socket()
+    with pytest.raises(wolfssl.SSLWantWriteError):
+        sock.write(b"data")
diff --git a/wolfssl/__init__.py b/wolfssl/__init__.py
index 7a739c3..c1754fb 100644
--- a/wolfssl/__init__.py
+++ b/wolfssl/__init__.py
@@ -590,6 +590,9 @@ class SSLSocket(object):
                 self.native_object, 0)
             if err == _SSL_ERROR_WANT_WRITE:
                 raise SSLWantWriteError()
+            elif err == _SSL_ERROR_WANT_READ:
+                # wolfSSL_write can require a read first (e.g. renegotiation).
+                raise SSLWantReadError()
             else:
                 raise SSLError(
                     "wolfSSL_write error (%d)" % err)