diff --git a/arango/formatter.py b/arango/formatter.py
index e159c23..568be24 100644
--- a/arango/formatter.py
+++ b/arango/formatter.py
@@ -119,6 +119,10 @@ def format_index(body: Json, formatter: bool = True) -> Json:
     # Introduced via Vector Index in 3.12.6
     if "params" in body:
         result["params"] = body["params"]
+    if "errorMessage" in body:
+        result["error_message"] = body["errorMessage"]
+    if "trainingState" in body:
+        result["training_state"] = body["trainingState"]
 
     return verify_format(body, result)
 
diff --git a/tests/static/cluster-3.12.conf b/tests/static/cluster-3.12.conf
index 3773711..6e325cc 100644
--- a/tests/static/cluster-3.12.conf
+++ b/tests/static/cluster-3.12.conf
@@ -9,6 +9,7 @@ jwt-secret = /tests/static/keyfile
 
 [args]
 all.database.password = passwd
+all.vector-index = true
 all.database.extended-names = true
 all.log.api-enabled = true
 all.javascript.allow-admin-execute = true
diff --git a/tests/static/single-3.12.conf b/tests/static/single-3.12.conf
index 3c43883..185ff7e 100644
--- a/tests/static/single-3.12.conf
+++ b/tests/static/single-3.12.conf
@@ -8,6 +8,7 @@ jwt-secret = /tests/static/keyfile
 
 [args]
 all.database.password = passwd
+all.vector-index = true
 all.database.extended-names = true
 all.javascript.allow-admin-execute = true
 all.server.options-api = admin
diff --git a/tests/test_index.py b/tests/test_index.py
index 04708d9..c756b1e 100644
--- a/tests/test_index.py
+++ b/tests/test_index.py
@@ -8,7 +8,7 @@
     IndexListError,
     IndexLoadError,
 )
-from tests.helpers import assert_raises, extract
+from tests.helpers import assert_raises, extract, generate_doc_key
 
 
 def test_list_indexes(icol, bad_col):
@@ -350,6 +350,27 @@ def test_add_mdi_index(icol, db_version):
     icol.delete_index(result["id"])
 
 
+def test_add_vector_index(col):
+    docs = []
+    for i in range(100):
+        docs.append({"_key": generate_doc_key(), "x": [1] * 128})
+    col.insert_many(docs)
+    result = col.add_index(
+        {
+            "type": "vector",
+            "fields": ["x"],
+            "name": "vector_index",
+            "params": {
+                "metric": "cosine",
+                "dimension": 128,
+                "nLists": 2,
+            },
+        }
+    )
+    assert result["name"] == "vector_index"
+    col.delete_index(result["id"])
+
+
 def test_delete_index(icol, bad_col):
     old_indexes = set(extract("id", icol.indexes()))
     hash_index = {"type": "hash", "fields": ["attr1", "attr2"], "unique": True}