diff --git a/doc/lua_api.md b/doc/lua_api.md
index ac22fe4ad..3f97af304 100644
--- a/doc/lua_api.md
+++ b/doc/lua_api.md
@@ -6126,9 +6126,11 @@ Environment access
 * `minetest.get_objects_inside_radius(center, radius)`
     * returns a list of ObjectRefs
     * `radius`: using a Euclidean metric
-    * **Warning**: If you modify objects (f.e. punch them),
-      this may cause later objects in the list (f.e. children) to become invalid.
-      Use `minetest.objects_inside_radius` instead to iterate only valid objects
+    * **Warning**: Any kind of interaction with the environment or other APIs
+      can cause later objects in the list to become invalid while you're iterating it.
+      (e.g. punching an entity removes its children)
+      It is recommend to use `minetest.objects_inside_radius` instead, which
+      transparently takes care of this possibility.
 * `minetest.objects_inside_radius(center, radius)`
     * returns an iterator of valid objects
     * example: `for obj in minetest.objects_inside_radius(center, radius) do obj:punch(...) end`
diff --git a/games/devtest/mods/unittests/entity.lua b/games/devtest/mods/unittests/entity.lua
index a6ce7c020..521076592 100644
--- a/games/devtest/mods/unittests/entity.lua
+++ b/games/devtest/mods/unittests/entity.lua
@@ -71,7 +71,7 @@ local function test_entity_lifecycle(_, pos)
 
 	-- with binary in staticdata
 	local obj = core.add_entity(pos, "unittests:callbacks", "abc\000def")
-	assert(obj:is_valid())
+	assert(obj and obj:is_valid())
 	check_log({"on_activate(7)"})
 
 	obj:set_hp(0)