diff --git a/invokeai/backend/ip_adapter/ip_adapter.py b/invokeai/backend/ip_adapter/ip_adapter.py
index 0f21cb9842..826112156d 100644
--- a/invokeai/backend/ip_adapter/ip_adapter.py
+++ b/invokeai/backend/ip_adapter/ip_adapter.py
@@ -86,7 +86,7 @@ class IPAdapter:
         self.attn_weights.to(device=self.device, dtype=self.dtype)
 
     def calc_size(self):
-        return calc_model_size_by_data(self._image_proj_model) + calc_model_size_by_data(self._attn_weights)
+        return calc_model_size_by_data(self._image_proj_model) + calc_model_size_by_data(self.attn_weights)
 
     def _init_image_proj_model(self, state_dict):
         return ImageProjModel.from_state_dict(state_dict, self._num_tokens).to(self.device, dtype=self.dtype)
diff --git a/invokeai/backend/ip_adapter/ip_attention_weights.py b/invokeai/backend/ip_adapter/ip_attention_weights.py
index 6eb1630890..e7ed9e9c76 100644
--- a/invokeai/backend/ip_adapter/ip_attention_weights.py
+++ b/invokeai/backend/ip_adapter/ip_attention_weights.py
@@ -22,25 +22,31 @@ class IPAttentionWeights(torch.nn.Module):
     forward(...) method.
     """
 
-    def __init__(self, weights: dict[int, IPAttentionProcessorWeights]):
+    def __init__(self, weights: torch.nn.ModuleDict):
         super().__init__()
-        self.weights = weights
+        self._weights = weights
 
     def set_scale(self, scale: float):
         """Set the scale (a.k.a. 'weight') for all of the `IPAttentionProcessorWeights` in this collection."""
-        for w in self.weights.values():
+        for w in self._weights.values():
             w.scale = scale
 
+    def get_attention_processor_weights(self, idx: int) -> IPAttentionProcessorWeights:
+        """Get the `IPAttentionProcessorWeights` for the idx'th attention processor."""
+        # Cast to int first, because we expect the key to represent an int. Then cast back to str, because
+        # `torch.nn.ModuleDict` only supports str keys.
+        return self._weights[str(int(idx))]
+
     @classmethod
     def from_state_dict(cls, state_dict: dict[str, torch.Tensor]):
-        attn_proc_weights: dict[int, IPAttentionProcessorWeights] = {}
+        attn_proc_weights: dict[str, IPAttentionProcessorWeights] = {}
 
         for tensor_name, tensor in state_dict.items():
             if "to_k_ip.weight" in tensor_name:
-                index = int(tensor_name.split(".")[0])
+                index = str(int(tensor_name.split(".")[0]))
                 attn_proc_weights[index] = IPAttentionProcessorWeights(tensor.shape[1], tensor.shape[0])
 
-        attn_proc_weights_module_dict = torch.nn.ModuleDict(attn_proc_weights)
-        attn_proc_weights_module_dict.load_state_dict(state_dict)
+        attn_proc_weights_module = torch.nn.ModuleDict(attn_proc_weights)
+        attn_proc_weights_module.load_state_dict(state_dict)
 
-        return cls(attn_proc_weights)
+        return cls(attn_proc_weights_module)
diff --git a/invokeai/backend/ip_adapter/unet_patcher.py b/invokeai/backend/ip_adapter/unet_patcher.py
index 17f3c4e595..ac9cf6de83 100644
--- a/invokeai/backend/ip_adapter/unet_patcher.py
+++ b/invokeai/backend/ip_adapter/unet_patcher.py
@@ -31,11 +31,14 @@ def _prepare_attention_processors(unet: UNet2DConditionModel, ip_adapters: list[
             attn_procs[name] = AttnProcessor2_0()
         else:
             # Collect the weights from each IP Adapter for the idx'th attention processor.
-            attn_procs[name] = IPAttnProcessor2_0([ip_adapter.attn_weights.weights[idx] for ip_adapter in ip_adapters])
+            attn_procs[name] = IPAttnProcessor2_0(
+                [ip_adapter.attn_weights.get_attention_processor_weights(idx) for ip_adapter in ip_adapters]
+            )
+    return attn_procs
 
 
 @contextmanager
-def apply_ip_adapter_attention(cls, unet: UNet2DConditionModel, ip_adapters: list[IPAdapter]):
+def apply_ip_adapter_attention(unet: UNet2DConditionModel, ip_adapters: list[IPAdapter]):
     """A context manager that patches `unet` with IP-Adapter attention processors."""
     attn_procs = _prepare_attention_processors(unet, ip_adapters)
 
diff --git a/tests/backend/ip_adapter/test_ip_adapter.py b/tests/backend/ip_adapter/test_ip_adapter.py
index 1248ead98b..f2ca243a93 100644
--- a/tests/backend/ip_adapter/test_ip_adapter.py
+++ b/tests/backend/ip_adapter/test_ip_adapter.py
@@ -1,6 +1,7 @@
 import pytest
 import torch
 
+from invokeai.backend.ip_adapter.unet_patcher import apply_ip_adapter_attention
 from invokeai.backend.model_management.models.base import BaseModelType, ModelType, SubModelType
 from invokeai.backend.util.test_utils import install_and_load_model
 
@@ -64,8 +65,8 @@ def test_ip_adapter_unet_patch(model_params, model_installer, torch_device):
         ip_adapter.to(torch_device, dtype=torch.float32)
         unet.to(torch_device, dtype=torch.float32)
 
-        cross_attention_kwargs = {"ip_adapter_image_prompt_embeds": torch.randn((1, 4, 768)).to(torch_device)}
-        with ip_adapter.apply_ip_adapter_attention(unet, 1.0):
+        cross_attention_kwargs = {"ip_adapter_image_prompt_embeds": [torch.randn((1, 4, 768)).to(torch_device)]}
+        with apply_ip_adapter_attention(unet, [ip_adapter]):
             output = unet(**dummy_unet_input, cross_attention_kwargs=cross_attention_kwargs).sample
 
     assert output.shape == dummy_unet_input["sample"].shape