diff --git a/src/nvim/api/vim.c b/src/nvim/api/vim.c
index 5a106288fd..a47694a0cf 100644
--- a/src/nvim/api/vim.c
+++ b/src/nvim/api/vim.c
@@ -2005,7 +2005,7 @@ Array nvim__inspect_cell(Integer grid, Integer row, Integer col, Arena *arena, E
   ADD_C(ret, DICTIONARY_OBJ(hl_get_attr_by_id(attr, true, arena, err)));
   // will not work first time
   if (!highlight_use_hlstate()) {
-    ADD_C(ret, ARRAY_OBJ(hl_inspect(attr)));
+    ADD_C(ret, ARRAY_OBJ(hl_inspect(attr, arena)));
   }
   return ret;
 }
diff --git a/src/nvim/highlight.c b/src/nvim/highlight.c
index 8b1c226851..1dc06ec988 100644
--- a/src/nvim/highlight.c
+++ b/src/nvim/highlight.c
@@ -116,12 +116,13 @@ retry: {}
   // new attr id, send event to remote ui:s
   int id = (int)k;
 
-  Array inspect = hl_inspect(id);
+  Arena arena = ARENA_EMPTY;
+  Array inspect = hl_inspect(id, &arena);
 
   // Note: internally we don't distinguish between cterm and rgb attributes,
   // remote_ui_hl_attr_define will however.
   ui_call_hl_attr_define(id, entry.attr, entry.attr, inspect);
-  api_free_array(inspect);
+  arena_mem_free(arena_finish(&arena));
   return id;
 }
 
@@ -129,10 +130,11 @@ retry: {}
 void ui_send_all_hls(UI *ui)
 {
   for (size_t i = 1; i < set_size(&attr_entries); i++) {
-    Array inspect = hl_inspect((int)i);
+    Arena arena = ARENA_EMPTY;
+    Array inspect = hl_inspect((int)i, &arena);
     HlAttrs attr = attr_entry(i).attr;
     remote_ui_hl_attr_define(ui, (Integer)i, attr, attr, inspect);
-    api_free_array(inspect);
+    arena_mem_free(arena_finish(&arena));
   }
   for (size_t hlf = 0; hlf < HLF_COUNT; hlf++) {
     remote_ui_hl_group_set(ui, cstr_as_string(hlf_names[hlf]),
@@ -204,7 +206,7 @@ int ns_get_hl(NS *ns_hl, int hl_id, bool link, bool nodefault)
   if (!valid_item && p->hl_def != LUA_NOREF && !recursive) {
     MAXSIZE_TEMP_ARRAY(args, 3);
     ADD_C(args, INTEGER_OBJ((Integer)ns_id));
-    ADD_C(args, CSTR_TO_OBJ(syn_id2name(hl_id)));
+    ADD_C(args, CSTR_AS_OBJ(syn_id2name(hl_id)));
     ADD_C(args, BOOLEAN_OBJ(link));
     // TODO(bfredl): preload the "global" attr dict?
 
@@ -1176,17 +1178,30 @@ int object_to_color(Object val, char *key, bool rgb, Error *err)
   }
 }
 
-Array hl_inspect(int attr)
+Array hl_inspect(int attr, Arena *arena)
 {
-  // TODO(bfredl): use arena allocation
-  Array ret = ARRAY_DICT_INIT;
-  if (hlstate_active) {
-    hl_inspect_impl(&ret, attr);
+  if (!hlstate_active) {
+    return (Array)ARRAY_DICT_INIT;
   }
+  Array ret = arena_array(arena, hl_inspect_size(attr));
+  hl_inspect_impl(&ret, attr, arena);
   return ret;
 }
 
-static void hl_inspect_impl(Array *arr, int attr)
+static size_t hl_inspect_size(int attr)
+{
+  if (attr <= 0 || attr >= (int)set_size(&attr_entries)) {
+    return 0;
+  }
+
+  HlEntry e = attr_entry(attr);
+  if (e.kind == kHlCombine || e.kind == kHlBlend || e.kind == kHlBlendThrough) {
+    return hl_inspect_size(e.id1) + hl_inspect_size(e.id2);
+  }
+  return 1;
+}
+
+static void hl_inspect_impl(Array *arr, int attr, Arena *arena)
 {
   Dictionary item = ARRAY_DICT_INIT;
   if (attr <= 0 || attr >= (int)set_size(&attr_entries)) {
@@ -1196,35 +1211,36 @@ static void hl_inspect_impl(Array *arr, int attr)
   HlEntry e = attr_entry(attr);
   switch (e.kind) {
   case kHlSyntax:
-    PUT(item, "kind", CSTR_TO_OBJ("syntax"));
-    PUT(item, "hi_name",
-        CSTR_TO_OBJ(syn_id2name(e.id1)));
+    item = arena_dict(arena, 3);
+    PUT_C(item, "kind", CSTR_AS_OBJ("syntax"));
+    PUT_C(item, "hi_name", CSTR_AS_OBJ(syn_id2name(e.id1)));
     break;
 
   case kHlUI:
-    PUT(item, "kind", CSTR_TO_OBJ("ui"));
+    item = arena_dict(arena, 4);
+    PUT_C(item, "kind", CSTR_AS_OBJ("ui"));
     const char *ui_name = (e.id1 == -1) ? "Normal" : hlf_names[e.id1];
-    PUT(item, "ui_name", CSTR_TO_OBJ(ui_name));
-    PUT(item, "hi_name",
-        CSTR_TO_OBJ(syn_id2name(e.id2)));
+    PUT_C(item, "ui_name", CSTR_AS_OBJ(ui_name));
+    PUT_C(item, "hi_name", CSTR_AS_OBJ(syn_id2name(e.id2)));
     break;
 
   case kHlTerminal:
-    PUT(item, "kind", CSTR_TO_OBJ("term"));
+    item = arena_dict(arena, 2);
+    PUT_C(item, "kind", CSTR_AS_OBJ("term"));
     break;
 
   case kHlCombine:
   case kHlBlend:
   case kHlBlendThrough:
     // attribute combination is associative, so flatten to an array
-    hl_inspect_impl(arr, e.id1);
-    hl_inspect_impl(arr, e.id2);
+    hl_inspect_impl(arr, e.id1, arena);
+    hl_inspect_impl(arr, e.id2, arena);
     return;
 
   case kHlUnknown:
   case kHlInvalid:
     return;
   }
-  PUT(item, "id", INTEGER_OBJ(attr));
-  ADD(*arr, DICTIONARY_OBJ(item));
+  PUT_C(item, "id", INTEGER_OBJ(attr));
+  ADD_C(*arr, DICTIONARY_OBJ(item));
 }