diff --git a/src/maxdiffusion/checkpointing/z_image_checkpointer.py b/src/maxdiffusion/checkpointing/z_image_checkpointer.py
index 5f12b3f3e..42c009d30 100644
--- a/src/maxdiffusion/checkpointing/z_image_checkpointer.py
+++ b/src/maxdiffusion/checkpointing/z_image_checkpointer.py
@@ -229,6 +229,10 @@ def build_vae(self, vae_config: dict):
 
   def build_text_encoder(self, text_encoder_config: dict):
     """Qwen3 graph, its abstract params and their target shardings."""
+    # transformers 5.x moved `rope_theta` into `rope_parameters`.
+    rope_theta = (text_encoder_config.get("rope_parameters") or {}).get("rope_theta")
+    if rope_theta is None:
+      rope_theta = text_encoder_config["rope_theta"]
     qwen3_config = FlaxQwen3Config(
         vocab_size=text_encoder_config["vocab_size"],
         hidden_size=text_encoder_config["hidden_size"],
@@ -238,7 +242,7 @@ def build_text_encoder(self, text_encoder_config: dict):
         num_key_value_heads=text_encoder_config["num_key_value_heads"],
         head_dim=text_encoder_config["head_dim"],
         rms_norm_eps=text_encoder_config["rms_norm_eps"],
-        rope_theta=text_encoder_config["rope_theta"],
+        rope_theta=rope_theta,
         max_position_embeddings=text_encoder_config["max_position_embeddings"],
         dtype=self.config.weights_dtype,
     )
diff --git a/src/maxdiffusion/tests/z_image/z_image_checkpointer_test.py b/src/maxdiffusion/tests/z_image/z_image_checkpointer_test.py
new file mode 100644
index 000000000..5bbe4bcae
--- /dev/null
+++ b/src/maxdiffusion/tests/z_image/z_image_checkpointer_test.py
@@ -0,0 +1,73 @@
+"""
+Copyright 2026 Google LLC
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     https://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+"""Z-Image text encoder config handling, without downloading weights."""
+
+import types
+import unittest
+
+import jax.numpy as jnp
+from flax import nnx
+from transformers import AutoConfig
+
+from maxdiffusion.checkpointing.z_image_checkpointer import ZImageCheckpointer
+from maxdiffusion.utils.testing_utils import cpu_only
+
+_TINY_QWEN3 = {
+    "vocab_size": 64,
+    "hidden_size": 32,
+    "intermediate_size": 64,
+    "num_hidden_layers": 1,
+    "num_attention_heads": 2,
+    "num_key_value_heads": 1,
+    "head_dim": 16,
+    "rms_norm_eps": 1e-6,
+    "max_position_embeddings": 128,
+}
+
+
+@cpu_only
+class ZImageTextEncoderConfigTest(unittest.TestCase):
+
+  def setUp(self):
+    config = types.SimpleNamespace(weights_dtype=jnp.float32, logical_axis_rules=(), seed=0)
+    self.checkpointer = ZImageCheckpointer(config, mesh=None)
+
+  def _rope_theta(self, text_encoder_config):
+    graphdef, state, rest, _ = self.checkpointer.build_text_encoder(text_encoder_config)
+    return nnx.merge(graphdef, state, rest).config.rope_theta
+
+  def test_rope_theta_top_level(self):
+    """transformers 4.x writes rope_theta at the top level of the config dict."""
+    self.assertEqual(self._rope_theta({**_TINY_QWEN3, "rope_theta": 12345.0}), 12345.0)
+
+  def test_rope_theta_in_rope_parameters(self):
+    """transformers 5.x keeps rope_theta only under rope_parameters."""
+    text_encoder_config = {**_TINY_QWEN3, "rope_parameters": {"rope_type": "default", "rope_theta": 12345.0}}
+    self.assertEqual(self._rope_theta(text_encoder_config), 12345.0)
+
+  def test_missing_rope_theta_raises(self):
+    with self.assertRaises(KeyError):
+      self._rope_theta({**_TINY_QWEN3, "rope_parameters": {"rope_type": "default"}})
+
+  def test_rope_theta_from_installed_transformers(self):
+    """The loader passes `AutoConfig.from_pretrained(...).to_dict()`, whichever layout it uses."""
+    text_encoder_config = AutoConfig.for_model("qwen3", **_TINY_QWEN3, rope_theta=12345.0).to_dict()
+    self.assertEqual(self._rope_theta(text_encoder_config), 12345.0)
+
+
+if __name__ == "__main__":
+  unittest.main()