diff --git a/nipreps/synthstrip/model.py b/nipreps/synthstrip/model.py
index 3081d2d..74eba9c 100644
--- a/nipreps/synthstrip/model.py
+++ b/nipreps/synthstrip/model.py
@@ -89,7 +89,7 @@ def __init__(
             max_pool = [max_pool] * self.nb_levels
 
         # cache downsampling / upsampling operations
-        MaxPooling = getattr(nn, 'MaxPool%dd' % ndims)
+        MaxPooling = getattr(nn, f'MaxPool{ndims}d')
         self.pooling = [MaxPooling(s) for s in max_pool]
         self.upsampling = [nn.Upsample(scale_factor=s, mode='nearest') for s in max_pool]
 
@@ -164,7 +164,7 @@ class ConvBlock(nn.Module):
     def __init__(self, ndims, in_channels, out_channels, stride=1, activation='leaky'):
         super().__init__()
 
-        Conv = getattr(nn, 'Conv%dd' % ndims)
+        Conv = getattr(nn, f'Conv{ndims}d')
         self.conv = Conv(in_channels, out_channels, 3, stride, 1)
         if activation == 'leaky':
             self.activation = nn.LeakyReLU(0.2)
diff --git a/nipreps/synthstrip/wrappers/nipype.py b/nipreps/synthstrip/wrappers/nipype.py
index 2362916..6fe2d85 100644
--- a/nipreps/synthstrip/wrappers/nipype.py
+++ b/nipreps/synthstrip/wrappers/nipype.py
@@ -23,6 +23,7 @@
 """SynthStrip interface."""
 
 import os
+from contextlib import suppress
 from pathlib import Path
 
 from nipype.interfaces.base import (
@@ -37,8 +38,10 @@
 _fs_home = os.getenv('FREESURFER_HOME', None)
 _default_model_path = Path(_fs_home) / 'models' / 'synthstrip.1.pt' if _fs_home else Undefined
 
-if _fs_home and not _default_model_path.exists():
-    _default_model_path = Undefined
+use_defaultmodel = False
+with suppress(AttributeError):
+    use_defaultmodel = _default_model_path.exists()
+    _default_model_path = str(_default_model_path)
 
 
 class _SynthStripInputSpec(CommandLineInputSpec):
@@ -50,8 +53,8 @@ class _SynthStripInputSpec(CommandLineInputSpec):
     )
     use_gpu = traits.Bool(False, usedefault=True, argstr='-g', desc='Use GPU', nohash=True)
     model = File(
-        str(_default_model_path),
-        usedefault=True,
+        _default_model_path,
+        usedefault=use_defaultmodel,
         exists=True,
         argstr='--model %s',
         desc="file containing model's weights",