diff --git a/Eigen/src/Core/products/Parallelizer.h b/Eigen/src/Core/products/Parallelizer.h
index 304dc7ed0..6e15e0ff5 100644
--- a/Eigen/src/Core/products/Parallelizer.h
+++ b/Eigen/src/Core/products/Parallelizer.h
@@ -51,6 +51,7 @@ void ei_parallelize_gemm(const Functor& func, int rows, int cols)
   // - the sizes are large enough
 
   // 1- are we already in a parallel session?
+  // FIXME omp_get_num_threads()>1 only works for openmp, what if the user does not use openmp?
   if((!Condition) || (omp_get_num_threads()>1))
     return func(0,rows, 0,cols);