diff --git a/diesel/src/pg/expression/operators.rs b/diesel/src/pg/expression/operators.rs
index dc6100694b98..f2d0934482b6 100644
--- a/diesel/src/pg/expression/operators.rs
+++ b/diesel/src/pg/expression/operators.rs
@@ -107,7 +107,9 @@ where
         &'b self,
         mut out: crate::query_builder::AstPass<'_, 'b, Pg>,
     ) -> crate::result::QueryResult<()> {
+        out.push_sql("(");
         self.array_expr.walk_ast(out.reborrow())?;
+        out.push_sql(")");
         out.push_sql("[");
         self.index_expr.walk_ast(out.reborrow())?;
         out.push_sql("]");
@@ -115,15 +117,40 @@ where
     }
 }
 
+// we cannot use the additional
+// parenthesis for updates
+#[derive(Debug)]
+pub struct UpdateArrayIndex<L, R>(ArrayIndex<L, R>);
+
+impl<L, R> QueryFragment<Pg> for UpdateArrayIndex<L, R>
+where
+    L: QueryFragment<Pg>,
+    R: QueryFragment<Pg>,
+{
+    fn walk_ast<'b>(
+        &'b self,
+        mut out: crate::query_builder::AstPass<'_, 'b, Pg>,
+    ) -> crate::result::QueryResult<()> {
+        self.0.array_expr.walk_ast(out.reborrow())?;
+        out.push_sql("[");
+        self.0.index_expr.walk_ast(out.reborrow())?;
+        out.push_sql("]");
+        Ok(())
+    }
+}
+
 impl<L, R> AssignmentTarget for ArrayIndex<L, R>
 where
     L: Column,
 {
     type Table = <L as Column>::Table;
-    type QueryAstNode = ArrayIndex<UncorrelatedColumn<L>, R>;
+    type QueryAstNode = UpdateArrayIndex<UncorrelatedColumn<L>, R>;
 
     fn into_target(self) -> Self::QueryAstNode {
-        ArrayIndex::new(UncorrelatedColumn(self.array_expr), self.index_expr)
+        UpdateArrayIndex(ArrayIndex::new(
+            UncorrelatedColumn(self.array_expr),
+            self.index_expr,
+        ))
     }
 }
 
diff --git a/diesel_tests/tests/index.rs b/diesel_tests/tests/index.rs
new file mode 100644
index 000000000000..3bbfb3913490
--- /dev/null
+++ b/diesel_tests/tests/index.rs
@@ -0,0 +1,13 @@
+#[cfg(feature = "postgres")]
+#[test]
+fn test_array_index() {
+    use diesel::dsl::array_append;
+    use diesel::sql_types::{Array, Integer};
+    use diesel::{PgArrayExpressionMethods, RunQueryDsl};
+    let connection = &mut crate::schema::connection();
+    let result = diesel::select(array_append::<Array<_>, Integer, _, _>(vec![1, 2, 3], 4).index(4))
+        .get_result::<i32>(connection)
+        .unwrap();
+
+    assert_eq!(4, result);
+}
diff --git a/diesel_tests/tests/lib.rs b/diesel_tests/tests/lib.rs
index 3df6e6e4f056..07743347201f 100644
--- a/diesel_tests/tests/lib.rs
+++ b/diesel_tests/tests/lib.rs
@@ -28,6 +28,7 @@ mod filter_operators;
 mod find;
 mod group_by;
 mod having;
+mod index;
 mod insert;
 mod insert_from_select;
 mod instrumentation;