diff --git a/include/boost/unordered/detail/foa/concurrent_table.hpp b/include/boost/unordered/detail/foa/concurrent_table.hpp
index b79f70c6..7fc397cc 100644
--- a/include/boost/unordered/detail/foa/concurrent_table.hpp
+++ b/include/boost/unordered/detail/foa/concurrent_table.hpp
@@ -840,8 +840,7 @@ private:
   using multimutex_type=multimutex<mutex_type,128>; // TODO: adapt 128 to the machine
   using shared_lock_guard=reentrancy_checked<shared_lock<mutex_type>>;
   using exclusive_lock_guard=reentrancy_checked<lock_guard<multimutex_type>>;
-  using exclusive_bilock_guard=
-    reentrancy_checked<reentrancy_checked<scoped_bilock<multimutex_type>>>;
+  using exclusive_bilock_guard=reentrancy_bichecked<scoped_bilock<multimutex_type>>;
   using group_shared_lock_guard=typename group_access::shared_lock_guard;
   using group_exclusive_lock_guard=typename group_access::exclusive_lock_guard;
   using group_insert_counter_type=typename group_access::insert_counter_type;
diff --git a/include/boost/unordered/detail/foa/reentrancy_check.hpp b/include/boost/unordered/detail/foa/reentrancy_check.hpp
index 6db39f1a..b0e65c64 100644
--- a/include/boost/unordered/detail/foa/reentrancy_check.hpp
+++ b/include/boost/unordered/detail/foa/reentrancy_check.hpp
@@ -56,10 +56,11 @@ class entry_trace
 public:
   entry_trace(const void* px_):px{px_}
   {
-    BOOST_ASSERT(px!=nullptr);
-    BOOST_UNORDERED_REENTRANCY_CHECK_ASSERT_MSG(
-      !find(px),"reentrancy not allowed");
-    header()=this;
+    if(px){
+      BOOST_UNORDERED_REENTRANCY_CHECK_ASSERT_MSG(
+        !find(px),"reentrancy not allowed");
+      header()=this;
+    }
   }
 
   /* not used but VS in pre-C++17 mode needs to see it for RVO */
@@ -111,6 +112,24 @@ struct reentrancy_checked
   LockGuard   lck;
 };
 
+template<typename LockGuard>
+struct reentrancy_bichecked
+{
+  template<typename... Args>
+  reentrancy_bichecked(const void* px,const void* py,Args&&... args):
+    tr1{px},tr2{py!=px?py:nullptr},lck{std::forward<Args>(args)...}{}
+
+  void unlock()
+  {
+    lck.unlock();
+    tr2.clear();
+    tr1.clear();
+  }
+
+  entry_trace tr1,tr2;
+  LockGuard   lck;
+};
+
 #else
 
 template<typename LockGuard>
@@ -125,6 +144,18 @@ struct reentrancy_checked
   LockGuard lck;
 };
 
+template<typename LockGuard>
+struct reentrancy_bichecked
+{
+  template<typename... Args>
+  reentrancy_bichecked(const void*,const void*,Args&&... args):
+    lck{std::forward<Args>(args)...}{}
+
+  void unlock(){lck.unlock();}
+
+  LockGuard lck;
+};
+
 #endif
 
 } /* namespace foa */