diff --git a/src/google/protobuf/descriptor.cc b/src/google/protobuf/descriptor.cc
index f194fadf9e..fc1ac2e09f 100644
--- a/src/google/protobuf/descriptor.cc
+++ b/src/google/protobuf/descriptor.cc
@@ -258,6 +258,16 @@ using IntT = int;
 template <typename T>
 using PointerT = T*;
 
+// State that we gather during EstimatedMemoryUsed while on the lock, but we
+// will use outside the lock.
+struct EstimatedMemoryUsedState {
+  // We can't call SpaceUsed under the lock because it uses reflection and can
+  // potentially deadlock if it requires to load new files into the pool.
+  // NOTE: Messages added here must not be modified or destroyed outside the
+  // lock while the pool is alive.
+  std::vector<const Message*> messages;
+};
+
 // Manages an allocation of sequential arrays of type `T...`.
 // It is more space efficient than storing N (ptr, size) pairs, by storing only
 // the pointer to the head and the boundaries between the arrays.
diff --git a/src/google/protobuf/late_loaded_option.proto b/src/google/protobuf/late_loaded_option.proto
new file mode 100644
index 0000000000..6fc30166f1
--- /dev/null
+++ b/src/google/protobuf/late_loaded_option.proto
@@ -0,0 +1,13 @@
+edition = "2023";
+
+package protobuf_unittest;
+
+import "google/protobuf/descriptor.proto";
+
+message LateLoadedOption {
+  int32 value = 1;
+
+  extend google.protobuf.MessageOptions {
+    LateLoadedOption ext = 95126892;
+  }
+}
diff --git a/src/google/protobuf/late_loaded_option_user.proto b/src/google/protobuf/late_loaded_option_user.proto
new file mode 100644
index 0000000000..f969af216a
--- /dev/null
+++ b/src/google/protobuf/late_loaded_option_user.proto
@@ -0,0 +1,11 @@
+edition = "2023";
+
+package protobuf_unittest;
+
+import "google/protobuf/late_loaded_option.proto";
+
+message LateLoadedOptionUser {
+  option (protobuf_unittest.LateLoadedOption.ext) = {
+    value: 1
+  };
+}