diff --git a/lib/bullet/src/BulletDynamics/Dynamics/btRigidBody.cpp b/lib/bullet/src/BulletDynamics/Dynamics/btRigidBody.cpp
index e077b535b..c052dd2de 100644
--- a/lib/bullet/src/BulletDynamics/Dynamics/btRigidBody.cpp
+++ b/lib/bullet/src/BulletDynamics/Dynamics/btRigidBody.cpp
@@ -82,7 +82,7 @@ void	btRigidBody::setupRigidBody(const btRigidBody::btRigidBodyConstructionInfo&
 
 	setCollisionShape( constructionInfo.m_collisionShape );
 	m_debugBodyId = uniqueId++;
-	
+	btAssert(constructionInfo.m_mass>=0);
 	setMassProps(constructionInfo.m_mass, constructionInfo.m_localInertia);
 	updateInertiaTensor();
 
diff --git a/src/physics/physical_object.cpp b/src/physics/physical_object.cpp
index 19e127701..1e9ebb9f4 100644
--- a/src/physics/physical_object.cpp
+++ b/src/physics/physical_object.cpp
@@ -91,7 +91,7 @@ void PhysicalObject::Settings::init()
     m_body_type          = PhysicalObject::MP_NONE;
     m_crash_reset        = false;
     m_knock_kart         = false;
-    m_mass               = -1.0f;
+    m_mass               = 0.0f;
     m_radius             = -1.0f;
     m_reset_when_too_low = false;
     m_flatten_kart       = false;