diff --git a/src/transport/xqc_conn.c b/src/transport/xqc_conn.c
index 8f7dc999d..95ef729b1 100644
--- a/src/transport/xqc_conn.c
+++ b/src/transport/xqc_conn.c
@@ -6500,6 +6500,16 @@ xqc_conn_set_early_remote_transport_params(xqc_connection_t *conn,
     }
 
     xqc_settings_copy_from_transport_params(&conn->remote_settings, params);
+
+    /*
+     * RFC 9000 §7.4.1: a client MUST NOT use remembered values for
+     * max_ack_delay, ack_delay_exponent, or stateless_reset_token.
+     * Reset them to defaults so the 0-RTT path never relies on stale values.
+     */
+    conn->remote_settings.max_ack_delay = XQC_DEFAULT_MAX_ACK_DELAY;
+    conn->remote_settings.ack_delay_exponent = XQC_DEFAULT_ACK_DELAY_EXPONENT;
+    conn->remote_settings.stateless_reset_token_present = 0;
+
     xqc_conn_update_flow_ctl_settings(conn);
     return XQC_OK;
 }
diff --git a/tests/unittest/main.c b/tests/unittest/main.c
index ed5343150..8658f64b7 100644
--- a/tests/unittest/main.c
+++ b/tests/unittest/main.c
@@ -228,6 +228,8 @@ main()
                         xqc_test_0rtt_params_all_increased)
         || !CU_add_test(pSuite, "xqc_test_0rtt_params_each_reduced",
                         xqc_test_0rtt_params_each_reduced)
+        || !CU_add_test(pSuite, "xqc_test_early_params_forbidden_fields_reset",
+                        xqc_test_early_params_forbidden_fields_reset)
         /* ALPN negotiation tests (issue #709) */
         || !CU_add_test(pSuite, "xqc_test_alpn_error_code_value",
                         xqc_test_alpn_error_code_value)
diff --git a/tests/unittest/xqc_conn_test.c b/tests/unittest/xqc_conn_test.c
index d7c05d9b3..5f7617215 100644
--- a/tests/unittest/xqc_conn_test.c
+++ b/tests/unittest/xqc_conn_test.c
@@ -635,6 +635,46 @@ xqc_test_0rtt_params_each_reduced(void)
 }
 
 
+/*
+ * RFC 9000 §7.4.1: client MUST NOT use remembered values for max_ack_delay,
+ * ack_delay_exponent, or stateless_reset_token.  Verify that
+ * xqc_conn_set_early_remote_transport_params resets them to defaults.
+ */
+void
+xqc_test_early_params_forbidden_fields_reset(void)
+{
+    xqc_connection_t *conn = test_engine_connect();
+    CU_ASSERT_FATAL(conn != NULL);
+
+    xqc_transport_params_t params;
+    memset(&params, 0, sizeof(params));
+
+    /* set forbidden fields to non-default values */
+    params.max_ack_delay = 100;  /* default is 25 */
+    params.ack_delay_exponent = 10;  /* default is 3 */
+    params.stateless_reset_token_present = 1;
+    memset(params.stateless_reset_token, 0xAB, sizeof(params.stateless_reset_token));
+
+    /* also set allowed fields */
+    params.initial_max_data = 65536;
+    params.initial_max_streams_bidi = 100;
+
+    xqc_int_t ret = xqc_conn_set_early_remote_transport_params(conn, &params);
+    CU_ASSERT_EQUAL(ret, XQC_OK);
+
+    /* forbidden fields must be reset to defaults */
+    CU_ASSERT_EQUAL(conn->remote_settings.max_ack_delay, XQC_DEFAULT_MAX_ACK_DELAY);
+    CU_ASSERT_EQUAL(conn->remote_settings.ack_delay_exponent, XQC_DEFAULT_ACK_DELAY_EXPONENT);
+    CU_ASSERT_EQUAL(conn->remote_settings.stateless_reset_token_present, 0);
+
+    /* allowed fields must be preserved */
+    CU_ASSERT_EQUAL(conn->remote_settings.max_data, 65536);
+    CU_ASSERT_EQUAL(conn->remote_settings.max_streams_bidi, 100);
+
+    xqc_engine_destroy(conn->engine);
+}
+
+
 void
 xqc_test_conn_tls_error_cb_max_alert()
 {
diff --git a/tests/unittest/xqc_conn_test.h b/tests/unittest/xqc_conn_test.h
index 4330ffb2a..18ad4e1fb 100644
--- a/tests/unittest/xqc_conn_test.h
+++ b/tests/unittest/xqc_conn_test.h
@@ -22,6 +22,9 @@ void xqc_test_0rtt_params_all_equal(void);
 void xqc_test_0rtt_params_all_increased(void);
 void xqc_test_0rtt_params_each_reduced(void);
 
+/* RFC 9000 §7.4.1: forbidden remembered fields must be reset (issue #672) */
+void xqc_test_early_params_forbidden_fields_reset(void);
+
 /* ALPN negotiation tests (issue #709) */
 void xqc_test_alpn_error_code_value(void);
 void xqc_test_alpn_server_cb_propagates_error(void);