diff --git a/related-packages/fileformats-extras/fileformats/extras/medimage_mrtrix3/image.py b/related-packages/fileformats-extras/fileformats/extras/medimage_mrtrix3/image.py
index 7ceaaa6..be543ee 100644
--- a/related-packages/fileformats-extras/fileformats/extras/medimage_mrtrix3/image.py
+++ b/related-packages/fileformats-extras/fileformats/extras/medimage_mrtrix3/image.py
@@ -13,7 +13,7 @@
 def generate_mrtrix_sample_data(
     mif: ImageFormat,
     generator: SampleFileGenerator,
-) -> ty.Iterable[Path]:
+) -> ty.List[Path]:
     nifti = Nifti1(get_dummy_nifti(generator.dest_dir / "nifti.nii"))
     with mock.patch.dict(os.environ, {"MRTRIX_CLI_PARSE_ONLY": "0"}):
         mif = ImageFormat.convert(nifti)
diff --git a/related-packages/fileformats-extras/fileformats/extras/medimage_mrtrix3/tracks.py b/related-packages/fileformats-extras/fileformats/extras/medimage_mrtrix3/tracks.py
index b192dc3..2ef9f37 100644
--- a/related-packages/fileformats-extras/fileformats/extras/medimage_mrtrix3/tracks.py
+++ b/related-packages/fileformats-extras/fileformats/extras/medimage_mrtrix3/tracks.py
@@ -11,7 +11,7 @@
 def generate_tracks_sample_data(
     tracks: Tracks,
     generator: SampleFileGenerator,
-) -> ty.Iterable[Path]:
+) -> ty.List[Path]:
     """Generate a tracks file with a single straight track of length 10"""
     fspath = generator.dest_dir / "tracks.tck"
     timestamp = str(time.time() * 1e9 + time.process_time_ns())
diff --git a/related-packages/fileformats/fileformats/medimage_mrtrix3/image.py b/related-packages/fileformats/fileformats/medimage_mrtrix3/image.py
index e41f126..8d1638e 100644
--- a/related-packages/fileformats/fileformats/medimage_mrtrix3/image.py
+++ b/related-packages/fileformats/fileformats/medimage_mrtrix3/image.py
@@ -65,7 +65,9 @@ def data_fspath(self):
 
     @property
     def data_offset(self):
-        return int(self.metadata["file"].split()[1])
+        fspath_and_offset = self.metadata["file"].split()
+        assert len(fspath_and_offset) <= 2
+        return int(fspath_and_offset[1]) if len(fspath_and_offset) > 1 else 0
 
     @property
     def vox_sizes(self):