diff --git a/docs/json_api.rst b/docs/json_api.rst
index c776bdb6..d234b852 100644
--- a/docs/json_api.rst
+++ b/docs/json_api.rst
@@ -549,6 +549,17 @@ To return the newly inserted rows, add the ``"return": true`` key to the request
 
 This will return the same ``"rows"`` key as the single row example above. There is a small performance penalty for using this option.
 
+If any of your rows have a primary key that is already in use, you will get an error and none of the rows will be inserted:
+
+.. code-block:: json
+
+    {
+        "ok": false,
+        "errors": [
+            "UNIQUE constraint failed: new_table.id"
+        ]
+    }
+
 .. _RowUpdateView:
 
 Updating a row
diff --git a/tests/test_api_write.py b/tests/test_api_write.py
index 330f8c5e..b3b1def2 100644
--- a/tests/test_api_write.py
+++ b/tests/test_api_write.py
@@ -168,7 +168,7 @@ async def test_write_rows(ds_write, return_rows):
         ),
         (
             "/data/docs/-/insert",
-            {"rows": [{"id": 1, "title": "Test"}]},
+            {"rows": [{"id": 1, "title": "Test"}, {"id": 2, "title": "Test"}]},
             "duplicate_id",
             400,
             ["UNIQUE constraint failed: docs.id"],
@@ -229,6 +229,9 @@ async def test_write_row_errors(
     if special_case == "invalid_json":
         del kwargs["json"]
         kwargs["content"] = "{bad json"
+    before_count = (
+        await ds_write.get_database("data").execute("select count(*) from docs")
+    ).rows[0][0] == 0
     response = await ds_write.client.post(
         path,
         **kwargs,
@@ -236,6 +239,11 @@ async def test_write_row_errors(
     assert response.status_code == expected_status
     assert response.json()["ok"] is False
     assert response.json()["errors"] == expected_errors
+    # Check that no rows were inserted
+    after_count = (
+        await ds_write.get_database("data").execute("select count(*) from docs")
+    ).rows[0][0] == 0
+    assert before_count == after_count
 
 
 @pytest.mark.asyncio