diff --git a/ruby/src/IceRuby/ValueFactoryManager.cpp b/ruby/src/IceRuby/ValueFactoryManager.cpp
index 0613bfd99e9..1f28638f239 100644
--- a/ruby/src/IceRuby/ValueFactoryManager.cpp
+++ b/ruby/src/IceRuby/ValueFactoryManager.cpp
@@ -88,7 +88,7 @@ IceRuby::ValueFactoryManager::add(Ice::ValueFactoryFunc, const string&)
 void
 IceRuby::ValueFactoryManager::add(const Ice::ValueFactoryPtr& f, const string& id)
 {
-    Lock lock(*this);
+    std::lock_guard lock(_mutex);
 
     if(id.empty())
     {
@@ -129,7 +129,7 @@ IceRuby::ValueFactoryManager::find(const string& id) const noexcept
 Ice::ValueFactoryPtr
 IceRuby::ValueFactoryManager::findCore(const string& id) const noexcept
 {
-    Lock lock(*this);
+    std::lock_guard lock(_mutex);
 
     if(id.empty())
     {
@@ -176,7 +176,7 @@ IceRuby::ValueFactoryManager::findValueFactory(const string& id) const
 void
 IceRuby::ValueFactoryManager::mark()
 {
-    Lock lock(*this);
+    std::lock_guard lock(_mutex);
 
     for(FactoryMap::iterator p = _factories.begin(); p != _factories.end(); ++p)
     {
@@ -196,7 +196,7 @@ IceRuby::ValueFactoryManager::markSelf()
     volatile VALUE self;
 
     {
-        Lock lock(*this);
+        std::lock_guard lock(_mutex);
 
         self = _self;
     }
@@ -219,7 +219,7 @@ IceRuby::ValueFactoryManager::destroy()
     FactoryMap factories;
 
     {
-        Lock lock(*this);
+        std::lock_guard lock(_mutex);
         if(_self == Qnil)
         {
             //
diff --git a/ruby/src/IceRuby/ValueFactoryManager.h b/ruby/src/IceRuby/ValueFactoryManager.h
index 5f31888755b..6fc5ba7d43d 100644
--- a/ruby/src/IceRuby/ValueFactoryManager.h
+++ b/ruby/src/IceRuby/ValueFactoryManager.h
@@ -55,7 +55,7 @@ class DefaultValueFactory : public Ice::ValueFactory
 };
 using DefaultValueFactoryPtr = std::shared_ptr<DefaultValueFactory>;
 
-class ValueFactoryManager final : public Ice::ValueFactoryManager, public IceUtil::Mutex
+class ValueFactoryManager final : public Ice::ValueFactoryManager
 {
 public:
 
@@ -88,6 +88,8 @@ class ValueFactoryManager final : public Ice::ValueFactoryManager, public IceUti
     VALUE _self;
     FactoryMap _factories;
     DefaultValueFactoryPtr _defaultFactory;
+
+    mutable std::mutex _mutex;
 };
 using ValueFactoryManagerPtr = std::shared_ptr<ValueFactoryManager>;