diff --git a/CMakeModules/CheckAtomicOps.cmake b/CMakeModules/CheckAtomicOps.cmake
index 3cd1876d8..773130f37 100644
--- a/CMakeModules/CheckAtomicOps.cmake
+++ b/CMakeModules/CheckAtomicOps.cmake
@@ -91,5 +91,5 @@ int main(int, const char**)
 " _OPENTHREADS_ATOMIC_USE_WIN32_INTERLOCKED)
 
 IF(NOT _OPENTHREADS_ATOMIC_USE_GCC_BUILTINS AND NOT _OPENTHREADS_ATOMIC_USE_MIPOSPRO_BUILTINS AND NOT _OPENTHREADS_ATOMIC_USE_SUN AND NOT _OPENTHREADS_ATOMIC_USE_WIN32_INTERLOCKED)
-  SET(_OPENTHREADS_ATOMIC_USE_MUTEX)
+  SET(_OPENTHREADS_ATOMIC_USE_MUTEX 1)
 ENDIF(NOT _OPENTHREADS_ATOMIC_USE_GCC_BUILTINS AND NOT _OPENTHREADS_ATOMIC_USE_MIPOSPRO_BUILTINS AND NOT _OPENTHREADS_ATOMIC_USE_SUN AND NOT _OPENTHREADS_ATOMIC_USE_WIN32_INTERLOCKED)
diff --git a/src/osg/Referenced.cpp b/src/osg/Referenced.cpp
index bac3b2c56..7e8fce9aa 100644
--- a/src/osg/Referenced.cpp
+++ b/src/osg/Referenced.cpp
@@ -82,10 +82,12 @@ struct DeleteHandlerPointer
 
 typedef std::set<Observer*> ObserverSet;
 
+#if defined(_OSG_REFERENCED_USE_ATOMIC_OPERATIONS)
 struct Referenced::ObserverSetData {
    OpenThreads::Mutex _mutex;
    ObserverSet _observers;
 };
+#endif
 
 #if !defined(_OSG_REFERENCED_USE_ATOMIC_OPERATIONS)
 static bool s_useThreadSafeReferenceCounting = getenv("OSG_THREAD_SAFE_REF_UNREF")!=0;