diff --git a/datasette/app.py b/datasette/app.py
index d7d20016..3a53afa5 100644
--- a/datasette/app.py
+++ b/datasette/app.py
@@ -450,7 +450,10 @@ class Datasette:
         for key in self._metadata_local or {}:
             if key == "databases":
                 continue
-            await self.set_instance_metadata(key, self._metadata_local[key])
+            value = self._metadata_local[key]
+            if not isinstance(value, str):
+                value = json.dumps(value)
+            await self.set_instance_metadata(key, value)
 
         # step 2: database-level metadata
         for dbname, db in self._metadata_local.get("databases", {}).items():
diff --git a/tests/test_internals_datasette.py b/tests/test_internals_datasette.py
index 135a9099..fc4e42cb 100644
--- a/tests/test_internals_datasette.py
+++ b/tests/test_internals_datasette.py
@@ -183,13 +183,16 @@ async def test_apply_metadata_json():
                 "legislators": {
                     "tables": {"offices": {"summary": "office address or sumtin"}},
                     "queries": {
-                        "millenntial_represetatives": {
+                        "millennial_representatives": {
                             "summary": "Social media accounts for current legislators"
                         }
                     },
                 }
-            }
+            },
+            "weird_instance_value": {"nested": [1, 2, 3]},
         },
     )
     await ds.invoke_startup()
     assert (await ds.client.get("/")).status_code == 200
+    value = (await ds.get_instance_metadata()).get("weird_instance_value")
+    assert value == '{"nested": [1, 2, 3]}'