diff --git a/src/core/ActionWithValue.cpp b/src/core/ActionWithValue.cpp
index 98d1c0810f31e0dc167cdcb0ef145e47f18dad7b..7a921ddbd941188b27365e8ad3d526823a80cd8c 100644
--- a/src/core/ActionWithValue.cpp
+++ b/src/core/ActionWithValue.cpp
@@ -70,7 +70,7 @@ void ActionWithValue::clearInputForces() {
 }
 
 void ActionWithValue::clearDerivatives() {
-  unsigned nt = OpenMP::getGoodNumThreads(values);
+  unsigned nt = OpenMP::getNumThreads(values);
   #pragma omp parallel num_threads(nt)
   {
     #pragma omp for
diff --git a/src/tools/OpenMP.h b/src/tools/OpenMP.h
index 43d9442e86c83bce0bae66d4bfa176050bac86bd..202f7ca58a11c445225ff85201a8eb6fa5479237 100644
--- a/src/tools/OpenMP.h
+++ b/src/tools/OpenMP.h
@@ -55,7 +55,7 @@ unsigned OpenMP::getGoodNumThreads(const T*x,unsigned n) {
   (void) p; // this is not to have warnings. notice that the pointer location is not used actually.
 // a factor two is necessary since there is no guarantee that x is aligned
 // to cache line boundary
-  unsigned m=n/(2*getCachelineSize()*sizeof(T));
+  unsigned m=n*sizeof(T)/(2*getCachelineSize());
   unsigned numThreads=getNumThreads();
   if(m>numThreads) m=numThreads;
   if(m==0) m=1;