diff --git a/src/pytom_tm/tmjob.py b/src/pytom_tm/tmjob.py
index 3200399d..566d3f51 100644
--- a/src/pytom_tm/tmjob.py
+++ b/src/pytom_tm/tmjob.py
@@ -44,6 +44,10 @@ def load_json_to_tmjob(
     with open(file_name, "r") as fstream:
         data = json.load(fstream)
 
+    # wrangle dtypes
+    output_dtype = data.get("output_dtype", "float32")
+    output_dtype = np.dtype(output_dtype)
+
     job = TMJob(
         data["job_key"],
         data["log_level"],
@@ -74,7 +78,7 @@ def load_json_to_tmjob(
         particle_diameter=data.get("particle_diameter", None),
         random_phase_correction=data.get("random_phase_correction", False),
         rng_seed=data.get("rng_seed", 321),
-        output_dtype=data.get("output_dtype", np.float32),
+        output_dtype=output_dtype,
     )
     # if the file originates from an old version set the phase shift for compatibility
     if (
@@ -527,6 +531,8 @@ def write_to_json(self, file_name: pathlib.Path) -> None:
         for key, value in d.items():
             if isinstance(value, pathlib.Path):
                 d[key] = str(value)
+            if isinstance(value, np.dtype):
+                d[key] = str(value)
         with open(file_name, "w") as fstream:
             json.dump(d, fstream, indent=4)