diff --git a/prism/prism.c b/prism/prism.c
index b85e31621ff416..2cde9fdd430f29 100644
--- a/prism/prism.c
+++ b/prism/prism.c
@@ -13767,6 +13767,9 @@ parse_write(pm_parser_t *parser, pm_node_t *target, pm_token_t *operator, pm_nod
 
                 // Replace the name with "[]=".
                 call->name = pm_parser_constant_id_constant(parser, "[]=", 3);
+
+                // Ensure that the arguments for []= don't contain keywords
+                pm_index_arguments_check(parser, call->arguments, NULL);
                 pm_node_flag_set((pm_node_t *) call, PM_CALL_NODE_FLAGS_ATTRIBUTE_WRITE | pm_implicit_array_write_flags(value, PM_CALL_NODE_FLAGS_IMPLICIT_ARRAY));
 
                 return target;