diff --git a/artiq/master/worker_db.py b/artiq/master/worker_db.py
index d2dd628f5..3a3f7ef25 100644
--- a/artiq/master/worker_db.py
+++ b/artiq/master/worker_db.py
@@ -173,8 +173,18 @@ class DatasetManager:
     def write_hdf5(self, f):
         datasets_group = f.create_group("datasets")
         for k, v in self.local.items():
-            datasets_group[k] = v
+            _write(datasets_group, k, v)
 
         archive_group = f.create_group("archive")
         for k, v in self.archive.items():
-            archive_group[k] = v
+            _write(archive_group, k, v)
+
+
+def _write(group, k, v):
+    # Add context to exception message when the user writes a dataset that is
+    # not representable in HDF5.
+    try:
+        group[k] = v
+    except TypeError as e:
+        raise TypeError("Error writing dataset '{}' of type '{}': {}".format(
+            k, type(v), e))