diff --git a/monai/networks/nets/diffusion_model_unet.py b/monai/networks/nets/diffusion_model_unet.py
index 113aa505e9..3e496979bf 100644
--- a/monai/networks/nets/diffusion_model_unet.py
+++ b/monai/networks/nets/diffusion_model_unet.py
@@ -33,8 +33,10 @@
 
 import math
 from collections.abc import Sequence
+from functools import reduce
 from typing import Optional
 
+import numpy as np
 import torch
 from torch import nn
 
@@ -1882,6 +1884,7 @@ class DiffusionModelEncoder(nn.Module):
         spatial_dims: number of spatial dimensions.
         in_channels: number of input channels.
         out_channels: number of output channels.
+        input_shape: spatial shape of the input (without batch and channel dims).
         num_res_blocks: number of residual blocks (see _ResnetBlock) per level.
         channels: tuple of block output channels.
         attention_levels: list of levels to add attention.
@@ -1901,6 +1904,7 @@ def __init__(
         spatial_dims: int,
         in_channels: int,
         out_channels: int,
+        input_shape: Sequence[int] = (64, 64),
         num_res_blocks: Sequence[int] | int = (2, 2, 2, 2),
         channels: Sequence[int] = (32, 64, 64, 64),
         attention_levels: Sequence[bool] = (False, False, True, True),
@@ -2007,7 +2011,14 @@ def __init__(
 
             self.down_blocks.append(down_block)
 
-        self.out: Optional[nn.Module] = None
+        for _ in channels:
+            input_shape = [int(np.ceil(i_ / 2)) for i_ in input_shape]
+
+        last_dim_flattened = int(reduce(lambda x, y: x * y, input_shape) * channels[-1])
+
+        self.out: Optional[nn.Module] = nn.Sequential(
+            nn.Linear(last_dim_flattened, 512), nn.ReLU(), nn.Dropout(0.1), nn.Linear(512, self.out_channels)
+        )
 
     def forward(
         self,
@@ -2052,10 +2063,9 @@ def forward(
         h = h.reshape(h.shape[0], -1)
 
         # 5. out
-        if self.out is None:
-            self.out = nn.Sequential(
-                nn.Linear(h.shape[1], 512), nn.ReLU(), nn.Dropout(0.1), nn.Linear(512, self.out_channels)
-            )
+        self.out = nn.Sequential(
+            nn.Linear(h.shape[1], 512), nn.ReLU(), nn.Dropout(0.1), nn.Linear(512, self.out_channels)
+        )
         output: torch.Tensor = self.out(h)
 
         return output