diff --git a/.python-version b/.python-version
new file mode 100644
index 00000000..cd94824d
--- /dev/null
+++ b/.python-version
@@ -0,0 +1,2 @@
+flask_wtf
+3.9.11
diff --git a/docs/changes.rst b/docs/changes.rst
index db77082e..3dcc41fa 100644
--- a/docs/changes.rst
+++ b/docs/changes.rst
@@ -1,6 +1,21 @@
 Changes
 =======
 
+Version 1.2.1.post2
+-------------
+
+Benchling-fork
+
+- Added logging when our custom deserialization is hit.
+
+Version 1.2.1.post1
+-------------
+
+Benchling-fork
+
+- Support deserializing old signed CSRF tokens
+
+
 Version 1.2.1
 -------------
 
diff --git a/pyproject.toml b/pyproject.toml
index ba5d915f..6aebcc9f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,5 +1,5 @@
 [project]
-name = "Flask-WTF"
+name = "benchling-flask-wtf"
 description = "Form rendering, validation, and CSRF protection for Flask with WTForms."
 readme = "README.rst"
 license = {file = "LICENSE.rst"}
diff --git a/src/flask_wtf/__init__.py b/src/flask_wtf/__init__.py
index be2649e2..16fd51e6 100644
--- a/src/flask_wtf/__init__.py
+++ b/src/flask_wtf/__init__.py
@@ -5,4 +5,4 @@
 from .recaptcha import RecaptchaField
 from .recaptcha import RecaptchaWidget
 
-__version__ = "1.2.1"
+__version__ = "1.2.1post2"
diff --git a/src/flask_wtf/csrf.py b/src/flask_wtf/csrf.py
index 06afa0cd..0588d92c 100644
--- a/src/flask_wtf/csrf.py
+++ b/src/flask_wtf/csrf.py
@@ -77,42 +77,112 @@ def validate_csrf(data, secret_key=None, time_limit=None, token_key=None):
 
     :raises ValidationError: Contains the reason that validation failed.
 
+    .. versionchanged:: 1.21.post1
+        Fallbacks to legacy_validate_csrf method. This provides a
+        compatibility layer for old clients.
     .. versionchanged:: 0.14
         Raises ``ValidationError`` with a specific error message rather than
         returning ``True`` or ``False``.
     """
+    try:
+        secret_key = _get_config(
+            secret_key,
+            "WTF_CSRF_SECRET_KEY",
+            current_app.secret_key,
+            message="A secret key is required to use CSRF.",
+        )
+        field_name = _get_config(
+            token_key,
+            "WTF_CSRF_FIELD_NAME",
+            "csrf_token",
+            message="A field name is required to use CSRF.",
+        )
+        time_limit = _get_config(time_limit, "WTF_CSRF_TIME_LIMIT", 3600, required=False)
 
-    secret_key = _get_config(
-        secret_key,
-        "WTF_CSRF_SECRET_KEY",
-        current_app.secret_key,
-        message="A secret key is required to use CSRF.",
-    )
-    field_name = _get_config(
-        token_key,
-        "WTF_CSRF_FIELD_NAME",
-        "csrf_token",
-        message="A field name is required to use CSRF.",
-    )
-    time_limit = _get_config(time_limit, "WTF_CSRF_TIME_LIMIT", 3600, required=False)
+        if not data:
+            raise ValidationError("The CSRF token is missing.")
+
+        if field_name not in session:
+            raise ValidationError("The CSRF session token is missing.")
 
-    if not data:
-        raise ValidationError("The CSRF token is missing.")
+        s = URLSafeTimedSerializer(secret_key, salt="wtf-csrf-token")
 
-    if field_name not in session:
-        raise ValidationError("The CSRF session token is missing.")
+        try:
+            token = s.loads(data, max_age=time_limit)
+        except SignatureExpired as e:
+            raise ValidationError("The CSRF token has expired.") from e
+        except BadData as e:
+            raise ValidationError("The CSRF token is invalid.") from e
+
+        if not hmac.compare_digest(session[field_name], token):
+            raise ValidationError("The CSRF tokens do not match.")
+    except Exception as e:
+        logger.info("Falling back to legacy CSRF validation.")
+        token_key = 'csrf_token' if token_key is None else token_key
+        is_valid = legacy_validate_csrf(
+            data=data,
+            secret_key=secret_key,
+            time_limit=time_limit,
+            token_key=token_key
+        )
+        if is_valid is False:
+            raise e
 
-    s = URLSafeTimedSerializer(secret_key, salt="wtf-csrf-token")
+
+def legacy_validate_csrf(data, secret_key=None, time_limit=None,
+                         token_key='csrf_token', url_safe=False):
+    """Validates CSRF tokens signed by flask_wtf < 0.14.
+
+    Taken from https://github.com/benchling/flask-wtf/blob/318eea7be584e1c1116fc9d010bbbe95ff0fde55/flask_wtf/csrf.py#L66-L114
+    """
+    import time
+
+    def to_bytes(text):
+        """Transform string to bytes."""
+        if isinstance(text, str):
+            text = text.encode('utf-8')
+        return text
+
+    delimiter = '--' if url_safe else '##'
+    if not data or delimiter not in data:
+        return False
 
     try:
-        token = s.loads(data, max_age=time_limit)
-    except SignatureExpired as e:
-        raise ValidationError("The CSRF token has expired.") from e
-    except BadData as e:
-        raise ValidationError("The CSRF token is invalid.") from e
-
-    if not hmac.compare_digest(session[field_name], token):
-        raise ValidationError("The CSRF tokens do not match.")
+        expires, hmac_csrf = data.split(delimiter, 1)
+    except ValueError:
+        return False  # unpack error
+
+    if time_limit is None:
+        time_limit = current_app.config.get('WTF_CSRF_TIME_LIMIT', 3600)
+
+    if time_limit:
+        try:
+            expires = int(expires)
+        except ValueError:
+            return False
+
+        now = int(time.time())
+        if now > expires:
+            return False
+
+    if not secret_key:
+        secret_key = current_app.config.get(
+            'WTF_CSRF_SECRET_KEY', current_app.secret_key
+        )
+
+    if token_key not in session:
+        return False
+
+    csrf_build = '%s%s' % (session[token_key], expires)
+    hmac_compare = hmac.new(
+        to_bytes(secret_key),
+        to_bytes(csrf_build),
+        digestmod=hashlib.sha1
+    ).hexdigest()
+
+    # Originally used werkzeug.security.safe_str_cmp, which was removed in Werkzeug 2.1
+    # https://github.com/pallets/werkzeug/pull/2276/files#diff-97d9d852b7ac5531335c7fdcb2b7e445c9d1d2993d02d56f129202fcdfcafbf3L103-L120
+    return hmac.compare_digest(hmac_compare, hmac_csrf)
 
 
 def _get_config(
diff --git a/tests/test_csrf_extension.py b/tests/test_csrf_extension.py
index 1a760b84..a029aca0 100644
--- a/tests/test_csrf_extension.py
+++ b/tests/test_csrf_extension.py
@@ -1,12 +1,14 @@
 import pytest
 from flask import Blueprint
-from flask import g
+from flask import g, session
 from flask import render_template_string
 
 from flask_wtf import FlaskForm
 from flask_wtf.csrf import CSRFError
 from flask_wtf.csrf import CSRFProtect
-from flask_wtf.csrf import generate_csrf
+from flask_wtf.csrf import generate_csrf, validate_csrf
+
+
 
 
 @pytest.fixture
@@ -30,6 +32,24 @@ def csrf(app):
     return app.extensions["csrf"]
 
 
+def test_validate_csrf(app):
+    with app.test_request_context():
+        token = generate_csrf()
+        assert validate_csrf(token) is None
+
+
+def test_validate_csrf_legacy_flask_wtf_013(app):
+    # Test confirms we can validate csrf tokens generated by flask-wtf 0.13
+    with app.test_request_context():
+        session['csrf_token'] = "static csrf token"
+        legacy_token1 = "2147400000##8587b4e882f4f9ca8dbe764657a839b10b6ce782"
+        assert validate_csrf(legacy_token1, secret_key='dev') is None
+
+        legacy_token2 = "##12a714b52cf57340c08dcab228f89c453399a2b4"
+        assert validate_csrf(legacy_token2, time_limit=0, secret_key='dev') is None
+        del session['csrf_token']
+
+
 def test_render_token(req_ctx):
     token = generate_csrf()
     assert render_template_string("{{ csrf_token() }}") == token
@@ -190,5 +210,5 @@ def assert_info(message):
     monkeypatch.setattr(logger, "info", assert_info)
 
     client.post("/")
-    assert len(messages) == 1
-    assert messages[0] == "The CSRF token is missing."
+    assert len(messages) == 2
+    assert messages[1] == "The CSRF token is missing."
diff --git a/tests/test_csrf_form.py b/tests/test_csrf_form.py
index f8d81288..14a50fdd 100644
--- a/tests/test_csrf_form.py
+++ b/tests/test_csrf_form.py
@@ -94,5 +94,5 @@ def assert_info(message):
 
     monkeypatch.setattr(logger, "info", assert_info)
     FlaskForm().validate()
-    assert len(messages) == 1
-    assert messages[0] == "The CSRF token is missing."
+    assert len(messages) == 2
+    assert messages[1] == "The CSRF token is missing."