diff --git a/include/nlohmann/detail/input/json_sax.hpp b/include/nlohmann/detail/input/json_sax.hpp
index 5af853ac1..6fd0be52d 100644
--- a/include/nlohmann/detail/input/json_sax.hpp
+++ b/include/nlohmann/detail/input/json_sax.hpp
@@ -937,6 +937,8 @@ class json_sax_dom_parser : public json_sax_dom_error_state
     /// directly if the value was the one too many.
     void place_container(const frame& f, frame* enclosing, BasicJsonType&& value, const bool enclosing_is_innermost)
     {
+        // only a container with a slot may have no enclosing container
+        JSON_ASSERT(f.slot != nullptr || enclosing != nullptr);
         if (f.slot != nullptr)
         {
             *f.slot = std::move(value);
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index b40405363..b2f432922 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -16043,6 +16043,8 @@ class json_sax_dom_parser : public json_sax_dom_error_state
     /// directly if the value was the one too many.
     void place_container(const frame& f, frame* enclosing, BasicJsonType&& value, const bool enclosing_is_innermost)
     {
+        // only a container with a slot may have no enclosing container
+        JSON_ASSERT(f.slot != nullptr || enclosing != nullptr);
         if (f.slot != nullptr)
         {
             *f.slot = std::move(value);