diff --git a/httpx/auth.py b/httpx/auth.py
index e0ef50c..e412c57 100644
--- a/httpx/auth.py
+++ b/httpx/auth.py
@@ -6,7 +6,7 @@ import typing
 from base64 import b64encode
 from urllib.request import parse_http_list
 
-from .exceptions import ProtocolError
+from .exceptions import ProtocolError, RequestBodyUnavailable
 from .models import Request, Response
 from .utils import to_bytes, to_str, unquote
 
@@ -104,6 +104,8 @@ class DigestAuth(Auth):
         self.password = to_bytes(password)
 
     def __call__(self, request: Request) -> AuthFlow:
+        if not request.stream.can_replay():
+            raise RequestBodyUnavailable("Request body is no longer available.")
         response = yield request
 
         if response.status_code != 401 or "www-authenticate" not in response.headers:

diff --git a/tests/client/test_auth.py b/tests/client/test_auth.py
index ea6ff8a..34ec77e 100644
--- a/tests/client/test_auth.py
+++ b/tests/client/test_auth.py
@@ -5,7 +5,15 @@ import typing
 
 import pytest
 
-from httpx import URL, AsyncClient, DigestAuth, ProtocolError, Request, Response
+from httpx import (
+    URL,
+    AsyncClient,
+    DigestAuth,
+    ProtocolError,
+    Request,
+    RequestBodyUnavailable,
+    Response,
+)
 from httpx.auth import Auth, AuthFlow
 from httpx.config import CertTypes, TimeoutTypes, VerifyTypes
 from httpx.dispatch.base import Dispatcher
@@ -442,3 +450,16 @@ async def test_auth_history() -> None:
     assert resp2.history == [resp1]
 
     assert len(resp1.history) == 0
+
+
+@pytest.mark.asyncio
+async def test_digest_auth_unavailable_streaming_body():
+    url = "https://example.org/"
+    auth = DigestAuth(username="tomchristie", password="password123")
+    client = AsyncClient(dispatch=MockDispatch())
+
+    async def streaming_body():
+        yield b"Example request body"
+
+    with pytest.raises(RequestBodyUnavailable):
+        await client.post(url, data=streaming_body(), auth=auth)

DigestAuth should raise a clear error if the request cannot replay.
Our DigestAuth implementation cannot work with non-replayable requests.
We ought to raise a nice clear error if `request.stream.is_replayable` is not True.
tests/client/test_auth.py::test_digest_auth_unavailable_streaming_body
tests/client/test_auth.py::test_basic_auth tests/client/test_auth.py::test_basic_auth_in_url tests/client/test_auth.py::test_basic_auth_on_session tests/client/test_auth.py::test_custom_auth tests/client/test_auth.py::test_netrc_auth tests/client/test_auth.py::test_auth_header_has_priority_over_netrc tests/client/test_auth.py::test_trust_env_auth tests/client/test_auth.py::test_auth_hidden_url tests/client/test_auth.py::test_auth_hidden_header tests/client/test_auth.py::test_auth_invalid_type tests/client/test_auth.py::test_digest_auth_returns_no_auth_if_no_digest_header_in_response tests/client/test_auth.py::test_digest_auth_200_response_including_digest_auth_header tests/client/test_auth.py::test_digest_auth_401_response_without_digest_auth_header tests/client/test_auth.py::test_digest_auth[MD5-64-32] tests/client/test_auth.py::test_digest_auth[MD5-SESS-64-32] tests/client/test_auth.py::test_digest_auth[SHA-64-40] tests/client/test_auth.py::test_digest_auth[SHA-SESS-64-40] tests/client/test_auth.py::test_digest_auth[SHA-256-64-64] tests/client/test_auth.py::test_digest_auth[SHA-256-SESS-64-64] tests/client/test_auth.py::test_digest_auth[SHA-512-64-128] tests/client/test_auth.py::test_digest_auth[SHA-512-SESS-64-128] tests/client/test_auth.py::test_digest_auth_no_specified_qop tests/client/test_auth.py::test_digest_auth_qop_including_spaces_and_auth_returns_auth[auth, tests/client/test_auth.py::test_digest_auth_qop_including_spaces_and_auth_returns_auth[auth,auth-int] tests/client/test_auth.py::test_digest_auth_qop_including_spaces_and_auth_returns_auth[unknown,auth] tests/client/test_auth.py::test_digest_auth_qop_auth_int_not_implemented tests/client/test_auth.py::test_digest_auth_qop_must_be_auth_or_auth_int tests/client/test_auth.py::test_digest_auth_incorrect_credentials tests/client/test_auth.py::test_digest_auth_raises_protocol_error_on_malformed_header[Digest tests/client/test_auth.py::test_digest_auth_raises_protocol_error_on_malformed_header[realm="httpx@example.org", tests/client/test_auth.py::test_digest_auth_raises_protocol_error_on_malformed_header[DigestZ tests/client/test_auth.py::test_auth_history