diff --git a/CHANGELOG.md b/CHANGELOG.md
index 01676efe7c59..e463c55caf7c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Changed
 
 - The `set_jwt_issuer` governance action has been updated, and no longer accepts `key_filter` or `key_policy` arguments (#6450).
+- Nodes started in `Join` mode will shut down if they receive and unrecoverable condition such as `StartupSeqnoIsOld` when attempting to join (#6471).
 
 ### Removed
 
diff --git a/src/node/node_state.h b/src/node/node_state.h
index 485eb21d086e..ed85d2cf819f 100644
--- a/src/node/node_state.h
+++ b/src/node/node_state.h
@@ -591,7 +591,18 @@ namespace ccf
             return;
           }
 
-          if (status != HTTP_STATUS_OK)
+          if (status == HTTP_STATUS_BAD_REQUEST)
+          {
+            auto error_msg = fmt::format(
+              "Join request to {} returned 400 Bad Request: {}. Shutting "
+              "down node gracefully.",
+              config.join.target_rpc_address,
+              std::string(data.begin(), data.end()));
+            LOG_FAIL_FMT("{}", error_msg);
+            RINGBUFFER_WRITE_MESSAGE(
+              AdminMessage::fatal_error_msg, to_host, error_msg);
+          }
+          else if (status != HTTP_STATUS_OK)
           {
             const auto& location = headers.find(http::headers::LOCATION);
             if (
diff --git a/tests/infra/network.py b/tests/infra/network.py
index bf4c32eb36cc..93abc20e89be 100644
--- a/tests/infra/network.py
+++ b/tests/infra/network.py
@@ -905,8 +905,9 @@ def run_join_node(
                 )
             except TimeoutError as e:
                 LOG.error(f"New pending node {node.node_id} failed to join the network")
+                has_stopped = node.remote.check_done()
                 if stop_on_error:
-                    assert node.remote.check_done()
+                    assert has_stopped, "Node should have stopped"
                 node.stop()
                 out_path, err_path = node.get_logs()
                 if out_path is not None and err_path is not None:
@@ -920,7 +921,7 @@ def run_join_node(
                         if "Quote does not contain known enclave measurement" in error:
                             raise CodeIdNotFound from e
                         if "StartupSeqnoIsOld" in error:
-                            raise StartupSeqnoIsOld from e
+                            raise StartupSeqnoIsOld(has_stopped) from e
                         if "invalid cert on handshake" in error:
                             raise ServiceCertificateInvalid from e
                 raise
diff --git a/tests/reconfiguration.py b/tests/reconfiguration.py
index fa0df57d7da7..f3cada1ab143 100644
--- a/tests/reconfiguration.py
+++ b/tests/reconfiguration.py
@@ -864,10 +864,13 @@ def run_join_old_snapshot(args):
                     snapshots_dir=tmp_dir,
                     timeout=3,
                 )
-            except infra.network.StartupSeqnoIsOld:
+            except infra.network.StartupSeqnoIsOld as e:
                 LOG.info(
                     f"Node {new_node.local_node_id} started from old snapshot could not join the service, as expected"
                 )
+                assert e.args == (
+                    True,
+                ), "Node has stopped on receiving StartupSeqnoIsOld"
             else:
                 raise RuntimeError(
                     f"Node {new_node.local_node_id} started from old snapshot unexpectedly joined the service"
@@ -883,10 +886,13 @@ def run_join_old_snapshot(args):
                     from_snapshot=False,
                     timeout=3,
                 )
-            except infra.network.StartupSeqnoIsOld:
+            except infra.network.StartupSeqnoIsOld as e:
                 LOG.info(
                     f"Node {new_node.local_node_id} started without snapshot could not join the service, as expected"
                 )
+                assert e.args == (
+                    True,
+                ), "Node has stopped on receiving StartupSeqnoIsOld"
             else:
                 raise RuntimeError(
                     f"Node {new_node.local_node_id} started without snapshot unexpectedly joined the service successfully"