diff --git a/src/flask/app.py b/src/flask/app.py
index 7bc952b1..85306d7c 100644
--- a/src/flask/app.py
+++ b/src/flask/app.py
@@ -16,6 +16,7 @@ from werkzeug.exceptions import BadRequest
 from werkzeug.exceptions import BadRequestKeyError
 from werkzeug.exceptions import HTTPException
 from werkzeug.exceptions import InternalServerError
+from werkzeug.local import ContextVar
 from werkzeug.routing import BuildError
 from werkzeug.routing import Map
 from werkzeug.routing import MapAdapter
@@ -35,7 +36,6 @@ from .globals import _request_ctx_stack
 from .globals import g
 from .globals import request
 from .globals import session
-from .helpers import async_to_sync
 from .helpers import get_debug_flag
 from .helpers import get_env
 from .helpers import get_flashed_messages
@@ -1579,10 +1579,40 @@ class Flask(Scaffold):
         .. versionadded:: 2.0
         """
         if iscoroutinefunction(func):
-            return async_to_sync(func)
+            return self.async_to_sync(func)
 
         return func
 
+    def async_to_sync(
+        self, func: t.Callable[..., t.Coroutine]
+    ) -> t.Callable[..., t.Any]:
+        """Return a sync function that will run the coroutine function.
+
+        .. code-block:: python
+
+            result = app.async_to_sync(func)(*args, **kwargs)
+
+        Override this method to change how the app converts async code
+        to be synchronously callable.
+
+        .. versionadded:: 2.0
+        """
+        try:
+            from asgiref.sync import async_to_sync as asgiref_async_to_sync
+        except ImportError:
+            raise RuntimeError(
+                "Install Flask with the 'async' extra in order to use async views."
+            )
+
+        # Check that Werkzeug isn't using its fallback ContextVar class.
+        if ContextVar.__module__ == "werkzeug.local":
+            raise RuntimeError(
+                "Async cannot be used with this combination of Python "
+                "and Greenlet versions."
+            )
+
+        return asgiref_async_to_sync(func)
+
     def make_response(self, rv: ResponseReturnValue) -> Response:
         """Convert the return value from a view function to an instance of
         :attr:`response_class`.
diff --git a/src/flask/helpers.py b/src/flask/helpers.py
index 621d51e6..109f544f 100644
--- a/src/flask/helpers.py
+++ b/src/flask/helpers.py
@@ -10,7 +10,6 @@ from threading import RLock
 
 import werkzeug.utils
 from werkzeug.exceptions import NotFound
-from werkzeug.local import ContextVar
 from werkzeug.routing import BuildError
 from werkzeug.urls import url_quote
 
@@ -800,26 +799,3 @@ def is_ip(value: str) -> bool:
             return True
 
     return False
-
-
-def async_to_sync(func: t.Callable[..., t.Coroutine]) -> t.Callable[..., t.Any]:
-    """Return a sync function that will run the coroutine function *func*.
-
-    This can be used as so
-
-        result = async_to_async(func)(*args, **kwargs)
-    """
-    try:
-        from asgiref.sync import async_to_sync as asgiref_async_to_sync
-    except ImportError:
-        raise RuntimeError(
-            "Install Flask with the 'async' extra in order to use async views."
-        )
-
-    # Check that Werkzeug isn't using its fallback ContextVar class.
-    if ContextVar.__module__ == "werkzeug.local":
-        raise RuntimeError(
-            "Async cannot be used with this combination of Python & Greenlet versions."
-        )
-
-    return asgiref_async_to_sync(func)
diff --git a/tests/test_async.py b/tests/test_async.py
index 798eed85..26a91118 100644
--- a/tests/test_async.py
+++ b/tests/test_async.py
@@ -6,7 +6,6 @@ import pytest
 from flask import Blueprint
 from flask import Flask
 from flask import request
-from flask.helpers import async_to_sync
 
 pytest.importorskip("asgiref")
 
@@ -136,5 +135,6 @@ def test_async_before_after_request():
 
 @pytest.mark.skipif(sys.version_info >= (3, 7), reason="should only raise Python < 3.7")
 def test_async_runtime_error():
+    app = Flask(__name__)
     with pytest.raises(RuntimeError):
-        async_to_sync(None)
+        app.async_to_sync(None)