diff --git a/src/OpenMesh/Core/System/mostream.hh b/src/OpenMesh/Core/System/mostream.hh
index b6c72404..cb932fca 100644
--- a/src/OpenMesh/Core/System/mostream.hh
+++ b/src/OpenMesh/Core/System/mostream.hh
@@ -63,7 +63,7 @@
 #include <string>
 #include <algorithm>
 
-#if __cplusplus > 199711L or __GXX_EXPERIMENTAL_CXX0X__
+#if __cplusplus > 199711L || defined( __GXX_EXPERIMENTAL_CXX0X__ )
   #include <mutex>
 #endif
 
@@ -182,7 +182,7 @@ protected:
   virtual int sync() 
   {
     // If working on multiple threads, we need to serialize the output correctly (requires c++11 headers)
-    #if __cplusplus > 199711L or __GXX_EXPERIMENTAL_CXX0X__
+    #if __cplusplus > 199711L || defined( __GXX_EXPERIMENTAL_CXX0X__ )
        std::lock_guard<std::mutex> lck (serializer_);
     #endif
 
@@ -207,7 +207,7 @@ protected:
     char c = traits_type::to_char_type(_c);
 
     // If working on multiple threads, we need to serialize the output correctly (requires c++11 headers)
-    #if __cplusplus > 199711L or __GXX_EXPERIMENTAL_CXX0X__
+    #if __cplusplus > 199711L || defined( __GXX_EXPERIMENTAL_CXX0X__ )
        {
          std::lock_guard<std::mutex> lck (serializer_);
          buffer_.push_back(c);
@@ -257,7 +257,7 @@ private:
   bool         enabled_;
 
   // If working on multiple threads, we need to serialize the output correctly (requires c++11 headers)
-  #if __cplusplus > 199711L or __GXX_EXPERIMENTAL_CXX0X__
+  #if __cplusplus > 199711L || defined( __GXX_EXPERIMENTAL_CXX0X__ )
      std::mutex serializer_;
   #endif
 
diff --git a/src/OpenMesh/Tools/Decimater/DecimaterT.cc b/src/OpenMesh/Tools/Decimater/DecimaterT.cc
index 1918f085..7b155cfe 100644
--- a/src/OpenMesh/Tools/Decimater/DecimaterT.cc
+++ b/src/OpenMesh/Tools/Decimater/DecimaterT.cc
@@ -71,7 +71,7 @@ template<class Mesh>
 DecimaterT<Mesh>::DecimaterT(Mesh& _mesh) :
   BaseDecimaterT<Mesh>(_mesh),
     mesh_(_mesh),
-#if __cplusplus > 199711L or __GXX_EXPERIMENTAL_CXX0X__
+#if __cplusplus > 199711L || defined( __GXX_EXPERIMENTAL_CXX0X__ )
   heap_(nullptr)
 #else
   heap_(NULL)
@@ -171,7 +171,7 @@ size_t DecimaterT<Mesh>::decimate(size_t _n_collapses) {
   // initialize heap
   HeapInterface HI(mesh_, priority_, heap_position_);
 
-#if __cplusplus > 199711L or __GXX_EXPERIMENTAL_CXX0X__
+#if __cplusplus > 199711L || defined( __GXX_EXPERIMENTAL_CXX0X__ )
   heap_ = std::unique_ptr<DeciHeap>(new DeciHeap(HI));
 #else
   heap_ = std::auto_ptr<DeciHeap>(new DeciHeap(HI));
@@ -272,7 +272,7 @@ size_t DecimaterT<Mesh>::decimate_to_faces(size_t _nv, size_t _nf) {
 
   // initialize heap
   HeapInterface HI(mesh_, priority_, heap_position_);
-  #if __cplusplus > 199711L or __GXX_EXPERIMENTAL_CXX0X__
+  #if __cplusplus > 199711L || defined( __GXX_EXPERIMENTAL_CXX0X__ )
     heap_ = std::unique_ptr<DeciHeap>(new DeciHeap(HI));
   #else
     heap_ = std::auto_ptr<DeciHeap>(new DeciHeap(HI));
diff --git a/src/OpenMesh/Tools/Decimater/DecimaterT.hh b/src/OpenMesh/Tools/Decimater/DecimaterT.hh
index 49c8c1e6..58c938ac 100644
--- a/src/OpenMesh/Tools/Decimater/DecimaterT.hh
+++ b/src/OpenMesh/Tools/Decimater/DecimaterT.hh
@@ -166,7 +166,7 @@ private: //------------------------------------------------------- private data
   Mesh&      mesh_;
 
   // heap
-  #if __cplusplus > 199711L or __GXX_EXPERIMENTAL_CXX0X__
+  #if __cplusplus > 199711L || defined( __GXX_EXPERIMENTAL_CXX0X__ )
     std::unique_ptr<DeciHeap> heap_;
   #else
     std::auto_ptr<DeciHeap> heap_;