diff --git a/Eigen/src/Core/products/GeneralBlockPanelKernel.h b/Eigen/src/Core/products/GeneralBlockPanelKernel.h
index f7cbc7f63..f6120fd12 100644
--- a/Eigen/src/Core/products/GeneralBlockPanelKernel.h
+++ b/Eigen/src/Core/products/GeneralBlockPanelKernel.h
@@ -41,7 +41,9 @@ inline void manage_caching_sizes(Action action, std::ptrdiff_t* l1=0, std::ptrdi
 {
   static std::ptrdiff_t m_l1CacheSize = 0;
   static std::ptrdiff_t m_l2CacheSize = 0;
+#ifdef _OPENMP
   #pragma omp threadprivate(m_l1CacheSize,m_l2CacheSize)
+#endif
   if(m_l1CacheSize==0)
   {
     m_l1CacheSize = manage_caching_sizes_helper(queryL1CacheSize(),8 * 1024);