diff --git a/swiftsimio/metadata/objects.py b/swiftsimio/metadata/objects.py
index b47a7938..db0cdcec 100644
--- a/swiftsimio/metadata/objects.py
+++ b/swiftsimio/metadata/objects.py
@@ -377,7 +377,9 @@ def __init__(self, base_mass_table: np.array, mass_units: unyt.unyt_quantity):
 
         # TODO: Extract these names from the files themselves if possible.
 
-        for index, name in metadata.particle_types.particle_name_underscores.items():
+        for index, name in enumerate(
+            metadata.particle_types.particle_name_underscores.values()
+        ):
             try:
                 setattr(
                     self,
diff --git a/tests/test_data.py b/tests/test_data.py
index 1cc32d3e..232864d2 100644
--- a/tests/test_data.py
+++ b/tests/test_data.py
@@ -12,7 +12,7 @@
 
 import h5py
 
-from unyt import K
+from unyt import K, Msun
 from numpy import logical_and, isclose, float64
 from numpy import array as numpy_array
 
@@ -53,8 +53,8 @@ def test_time_metadata(filename):
 @requires("cosmological_volume.hdf5")
 def test_temperature_units(filename):
     """
-    This tests checks if we correctly read in temperature units. Based on a past bug, to make
-    sure we never break this again.
+    This tests checks if we correctly read in temperature units. Based
+    on a past bug, to make sure we never break this again.
     """
 
     data = load(filename)
@@ -63,6 +63,19 @@ def test_temperature_units(filename):
     return
 
 
+@requires("cosmological_volume.hdf5")
+def test_initial_mass_table(filename):
+    """
+    This tests checks if we correctly read in the initial mass table. Based
+    on a past bug, to make sure we never break this again.
+    """
+
+    data = load(filename)
+    data.metadata.initial_mass_table.gas.convert_to_units(Msun)
+
+    return
+
+
 @requires("cosmological_volume.hdf5")
 def test_units(filename):
     """