diff --git a/lib/nBodySim.cpp b/lib/nBodySim.cpp
index c47a32fa04ef4e4579e267b97011e6009f3f27ac..5a5353b9511052b36fb9c1705b71b1c6d84ba31e 100644
--- a/lib/nBodySim.cpp
+++ b/lib/nBodySim.cpp
@@ -114,6 +114,7 @@ void nBodySim::calculateForces() {
 }
 
 void nBodySim::treeCalculateForces() {
+    #pragma omp parallel for
     for (unsigned i=0; i < nParticles_; ++i) {
         tree_->calculateForce(i);
     }