diff --git a/sqlite-vec.c b/sqlite-vec.c
index db79d0b..53c4635 100644
--- a/sqlite-vec.c
+++ b/sqlite-vec.c
@@ -10055,6 +10055,26 @@ int vec0Update_Update(sqlite3_vtab *pVTab, int argc, sqlite3_value **argv) {
       continue;
     }
 
+    // Block vector UPDATE for index types that don't implement it —
+    // the DiskANN graph / IVF lists would become stale.
+    {
+      enum Vec0IndexType idx_type = p->vector_columns[vector_idx].index_type;
+      const char *idx_name = NULL;
+      if (idx_type == VEC0_INDEX_TYPE_DISKANN) idx_name = "DiskANN";
+#if SQLITE_VEC_EXPERIMENTAL_IVF_ENABLE
+      else if (idx_type == VEC0_INDEX_TYPE_IVF) idx_name = "IVF";
+#endif
+      if (idx_name) {
+        vtab_set_error(
+          &p->base,
+          "UPDATE on vector column \"%.*s\" is not supported for %s indexes.",
+          p->vector_columns[vector_idx].name_length,
+          p->vector_columns[vector_idx].name,
+          idx_name);
+        return SQLITE_ERROR;
+      }
+    }
+
     rc = vec0Update_UpdateVectorColumn(p, chunk_id, chunk_offset, vector_idx,
                                        valueVector, rowid);
     if (rc != SQLITE_OK) {
diff --git a/tests/test-diskann.py b/tests/test-diskann.py
index 4c049ce..4fad96b 100644
--- a/tests/test-diskann.py
+++ b/tests/test-diskann.py
@@ -891,7 +891,7 @@ def test_diskann_delete_preserves_graph_connectivity(db):
 # ======================================================================
 
 def test_diskann_update_vector(db):
-    """UPDATE a vector on DiskANN table may not be supported; verify it either works or errors cleanly."""
+    """UPDATE a vector on DiskANN table should error (will be implemented soon)."""
     db.execute("""
         CREATE VIRTUAL TABLE t USING vec0(
             emb float[8] INDEXED BY diskann(neighbor_quantizer=binary, n_neighbors=8)
@@ -901,17 +901,8 @@ def test_diskann_update_vector(db):
     db.execute("INSERT INTO t(rowid, emb) VALUES (2, ?)", [_f32([0, 1, 0, 0, 0, 0, 0, 0])])
     db.execute("INSERT INTO t(rowid, emb) VALUES (3, ?)", [_f32([0, 0, 1, 0, 0, 0, 0, 0])])
 
-    # UPDATE may not be fully supported for DiskANN yet; verify no crash
-    result = exec(db, "UPDATE t SET emb = ? WHERE rowid = 1", [_f32([0, 0.9, 0.1, 0, 0, 0, 0, 0])])
-    if "error" not in result:
-        # If UPDATE succeeded, verify KNN reflects the new value
-        rows = db.execute(
-            "SELECT rowid, distance FROM t WHERE emb MATCH ? AND k=3",
-            [_f32([0, 1, 0, 0, 0, 0, 0, 0])],
-        ).fetchall()
-        assert len(rows) == 3
-        # rowid 2 should still be closest (exact match)
-        assert rows[0][0] == 2
+    with pytest.raises(sqlite3.OperationalError, match="UPDATE on vector column.*not supported for DiskANN"):
+        db.execute("UPDATE t SET emb = ? WHERE rowid = 1", [_f32([0, 0.9, 0.1, 0, 0, 0, 0, 0])])
 
 
 # ======================================================================
diff --git a/tests/test-ivf-mutations.py b/tests/test-ivf-mutations.py
index 5c61119..fce1832 100644
--- a/tests/test-ivf-mutations.py
+++ b/tests/test-ivf-mutations.py
@@ -573,3 +573,15 @@ def test_interleaved_ops_correctness(db):
     # Verify we get the right count (25 odd + 15 new - 10 deleted new = 30)
     expected_alive = set(range(1, 50, 2)) | set(range(50, 60)) | set(range(70, 75))
     assert rowids.issubset(expected_alive)
+
+
+def test_ivf_update_vector_blocked(db):
+    """UPDATE on a vector column with IVF index should error (index would become stale)."""
+    db.execute(
+        "CREATE VIRTUAL TABLE t USING vec0(emb float[4] indexed by ivf(nlist=2))"
+    )
+    db.execute("INSERT INTO t(rowid, emb) VALUES (1, ?)", [_f32([1, 0, 0, 0])])
+    db.execute("INSERT INTO t(rowid, emb) VALUES (2, ?)", [_f32([0, 1, 0, 0])])
+
+    with pytest.raises(sqlite3.OperationalError, match="UPDATE on vector column.*not supported for IVF"):
+        db.execute("UPDATE t SET emb = ? WHERE rowid = 1", [_f32([0, 0, 1, 0])])