diff --git a/rllib/algorithms/bc/torch/bc_torch_rl_module.py b/rllib/algorithms/bc/torch/bc_torch_rl_module.py
index a547047d7f41..d06c323b124e 100644
--- a/rllib/algorithms/bc/torch/bc_torch_rl_module.py
+++ b/rllib/algorithms/bc/torch/bc_torch_rl_module.py
@@ -11,7 +11,7 @@ class BCTorchRLModule(TorchRLModule):
     @override(RLModule)
     def setup(self):
         # __sphinx_doc_begin__
-        # Build models from catalog
+        # Build models from catalog.
         self.encoder = self.catalog.build_encoder(framework=self.framework)
         self.pi = self.catalog.build_pi_head(framework=self.framework)
 
diff --git a/rllib/core/rl_module/multi_rl_module.py b/rllib/core/rl_module/multi_rl_module.py
index a447d084533b..43eddb909dea 100644
--- a/rllib/core/rl_module/multi_rl_module.py
+++ b/rllib/core/rl_module/multi_rl_module.py
@@ -1,5 +1,5 @@
 import copy
-from dataclasses import dataclass, field
+import dataclasses
 import logging
 import pprint
 from typing import (
@@ -666,7 +666,11 @@ def build(self, module_id: Optional[ModuleID] = None) -> RLModule:
                 observation_space=self.observation_space,
                 action_space=self.action_space,
                 inference_only=self.inference_only,
-                model_config=self.model_config,
+                model_config=(
+                    dataclasses.asdict(self.model_config)
+                    if dataclasses.is_dataclass(self.model_config)
+                    else self.model_config
+                ),
                 rl_module_specs=self.rl_module_specs,
             )
         # Older custom model might still require the old `MultiRLModuleConfig` under
@@ -859,7 +863,7 @@ def get_rl_module_config(self):
     "module2: [RLModuleSpec], ..}, inference_only=..)",
     error=False,
 )
-@dataclass
+@dataclasses.dataclass
 class MultiRLModuleConfig:
     inference_only: bool = False
     modules: Dict[ModuleID, RLModuleSpec] = dataclasses.field(default_factory=dict)
diff --git a/rllib/core/rl_module/rl_module.py b/rllib/core/rl_module/rl_module.py
index f1fb5b337cc5..42aa0a780ed4 100644
--- a/rllib/core/rl_module/rl_module.py
+++ b/rllib/core/rl_module/rl_module.py
@@ -98,7 +98,7 @@ def build(self) -> "RLModule":
                 observation_space=self.observation_space,
                 action_space=self.action_space,
                 inference_only=self.inference_only,
-                model_config=self.model_config,
+                model_config=self._get_model_config(),
                 catalog_class=self.catalog_class,
             )
         # Older custom model might still require the old `RLModuleConfig` under