diff --git a/Simulations/MassSpringSystemSimulator.cpp b/Simulations/MassSpringSystemSimulator.cpp
index c9e8026..fe9475c 100644
--- a/Simulations/MassSpringSystemSimulator.cpp
+++ b/Simulations/MassSpringSystemSimulator.cpp
@@ -328,7 +328,7 @@ void MassSpringSystemSimulator::Midpoint(Spring& spring, float timestep) {
 	Vec3 PosNorm1 = PosVector / d;
 	Vec3 PosNorm2 = -1 * PosNorm1;
 
-	Vec3 Force = -m_fStiffness * (d - springs.at(0).initialLength) * PosNorm1;
+	Vec3 Force = -m_fStiffness * (d - spring.initialLength) * PosNorm1;
 	Vec3 Force2 = -1 * Force;
 
 	Vec3 oldAcc = calculateAcceleration(Force,m_fMass);