diff --git a/mmseg/models/decode_heads/mask2former_head.py b/mmseg/models/decode_heads/mask2former_head.py
index 0ea742430..0135af064 100644
--- a/mmseg/models/decode_heads/mask2former_head.py
+++ b/mmseg/models/decode_heads/mask2former_head.py
@@ -4,12 +4,13 @@ from typing import List, Tuple
 import torch
 import torch.nn as nn
 import torch.nn.functional as F
+from mmengine.model import BaseModule
 
 try:
     from mmdet.models.dense_heads import \
         Mask2FormerHead as MMDET_Mask2FormerHead
 except ModuleNotFoundError:
-    MMDET_Mask2FormerHead = None
+    MMDET_Mask2FormerHead = BaseModule
 
 from mmengine.structures import InstanceData
 from torch import Tensor
diff --git a/mmseg/models/decode_heads/maskformer_head.py b/mmseg/models/decode_heads/maskformer_head.py
index 98ca92b99..6e61a7f63 100644
--- a/mmseg/models/decode_heads/maskformer_head.py
+++ b/mmseg/models/decode_heads/maskformer_head.py
@@ -4,11 +4,12 @@ from typing import List, Tuple
 import torch
 import torch.nn as nn
 import torch.nn.functional as F
+from mmengine.model import BaseModule
 
 try:
     from mmdet.models.dense_heads import MaskFormerHead as MMDET_MaskFormerHead
 except ModuleNotFoundError:
-    MMDET_MaskFormerHead = None
+    MMDET_MaskFormerHead = BaseModule
 
 from mmengine.structures import InstanceData
 from torch import Tensor