diff --git a/R/tunable.R b/R/tunable.R
index 244bbba30..675a22c79 100644
--- a/R/tunable.R
+++ b/R/tunable.R
@@ -4,7 +4,8 @@
 
 #' @export
 tunable.model_spec <- function(x, ...) {
-  mod_env <- rlang::ns_env("parsnip")$parsnip
+
+  mod_env <- get_model_env()
 
   if (is.null(x$engine)) {
     stop("Please declare an engine first using `set_engine()`.", call. = FALSE)
@@ -17,27 +18,35 @@ tunable.model_spec <- function(x, ...) {
          sep = "", call. = FALSE)
   }
 
-  arg_vals <-
-    mod_env[[arg_name]] %>%
-    dplyr::filter(engine == x$engine) %>%
-    dplyr::select(name = parsnip, call_info = func) %>%
-    dplyr::full_join(
-      tibble::tibble(name = c(names(x$args), names(x$eng_args))),
-      by = "name"
-    ) %>%
-    dplyr::mutate(
-      source = "model_spec",
-      component = mod_type(x),
-      component_id = dplyr::if_else(name %in% names(x$args), "main", "engine")
+  arg_vals <- mod_env[[arg_name]]
+  arg_vals <- arg_vals[arg_vals$engine == x$engine, c("parsnip", "func")]
+  names(arg_vals)[names(arg_vals) == "parsnip"] <- "name"
+  names(arg_vals)[names(arg_vals) == "func"] <- "call_info"
+
+  extra_args <- c(names(x$args), names(x$eng_args))
+  extra_args <- extra_args[!extra_args %in% arg_vals$name]
+
+  extra_args_tbl <-
+    tibble::new_tibble(
+      list(name = extra_args, call_info = vector("list", vctrs::vec_size(extra_args))),
+      nrow = vctrs::vec_size(extra_args)
     )
 
-  if (nrow(arg_vals) > 0) {
-    has_info <- purrr::map_lgl(arg_vals$call_info, is.null)
-    rm_list <- !(has_info & (arg_vals$component_id == "main"))
+  res <- vctrs::vec_rbind(arg_vals, extra_args_tbl)
 
-    arg_vals <- arg_vals[rm_list,]
+  res$source <- "model_spec"
+  res$component <- mod_type(x)
+  res$component_id <- "main"
+  res$component_id[!res$name %in% names(x$args)] <- "engine"
+
+  if (nrow(res) > 0) {
+    has_info <- purrr::map_lgl(res$call_info, is.null)
+    rm_list <- !(has_info & (res$component_id == "main"))
+
+    res <- res[rm_list, ]
   }
-  arg_vals %>% dplyr::select(name, call_info, source, component, component_id)
+
+  res[, c("name", "call_info", "source", "component", "component_id")]
 }
 
 mod_type <- function(.mod) class(.mod)[class(.mod) != "model_spec"][1]