diff --git a/openmc/source.py b/openmc/source.py
index 3863bb826a..b5b53167c5 100644
--- a/openmc/source.py
+++ b/openmc/source.py
@@ -308,9 +308,11 @@ def write_source_file(source_particles, filename, **kwargs):
     ])
 
     # Create array of source particles
+    cv.check_iterable_type("source particles", source_particles, SourceParticle)
     arr = np.array([s.to_tuple() for s in source_particles], dtype=source_dtype)
 
     # Write array to file
     kwargs.setdefault('mode', 'w')
     with h5py.File(filename, **kwargs) as fh:
+        fh.attrs['filetype'] = np.string_("source")
         fh.create_dataset('source_bank', data=arr, dtype=source_dtype)
diff --git a/tests/unit_tests/test_source_file.py b/tests/unit_tests/test_source_file.py
index e9bcebc92e..ae6eff97f7 100644
--- a/tests/unit_tests/test_source_file.py
+++ b/tests/unit_tests/test_source_file.py
@@ -3,9 +3,14 @@ from random import random
 import h5py
 import numpy as np
 import openmc
+import pytest
 
 
 def test_source_file(run_in_tmpdir):
+    # write_source_file shouldn't accept non-SourceParticle items
+    with pytest.raises(TypeError):
+        openmc.write_source_file([1, 2, 3], 'test_source.h5')
+
     # Create source particles
     source = []
     n = 1000
@@ -21,9 +26,11 @@ def test_source_file(run_in_tmpdir):
 
     # Get array of source particles from file
     with h5py.File('test_source.h5', 'r') as fh:
+        filetype = fh.attrs['filetype']
         arr = fh['source_bank'][...]
 
     # Ensure data is consistent
+    assert filetype == b'source'
     r = arr['r']
     assert np.all((r['x'] > 0.0) & (r['x'] < 1.0))
     assert np.all(r['y'] == np.arange(1000))