diff --git a/src/simulation/Simulation.cpp b/src/simulation/Simulation.cpp
index 2c8239513..c338932c6 100644
--- a/src/simulation/Simulation.cpp
+++ b/src/simulation/Simulation.cpp
@@ -3740,6 +3740,7 @@ void Simulation::BeforeSim()
 			air->update_airh();
 
 		DispatchNewtonianGravity();
+		// gravIn is now potentially garbage, which is ok, we were going to clear it for the frame anyway
 		for (auto p : gravIn.mass.Size().OriginRect())
 		{
 			gravIn.mass[p] = 0.f;
@@ -3964,6 +3965,8 @@ void Simulation::ResetNewtonianGravity(GravityInput newGravIn, GravityOutput new
 {
 	gravIn = newGravIn;
 	DispatchNewtonianGravity();
+	// gravIn is now potentially garbage, set it again
+	gravIn = newGravIn;
 	if (grav)
 	{
 		gravOut = newGravOut;
@@ -3981,7 +3984,10 @@ void Simulation::EnableNewtonianGravity(bool enable)
 	if (!grav && enable)
 	{
 		grav = Gravity::Create();
+		auto oldGravIn = gravIn;
 		DispatchNewtonianGravity();
+		// gravIn is now potentially garbage, set it again
+		gravIn = std::move(oldGravIn);
 	}
 }
 
diff --git a/src/simulation/Simulation.h b/src/simulation/Simulation.h
index e4ea5ae44..94dc66608 100644
--- a/src/simulation/Simulation.h
+++ b/src/simulation/Simulation.h
@@ -220,10 +220,11 @@ public:
 	~Simulation();
 
 	void EnableNewtonianGravity(bool enable);
-	void ResetNewtonianGravity(GravityInput newGravIn, GravityOutput newGravOut);
-	void DispatchNewtonianGravity();
-	void UpdateGravityMask();
 
 private:
 	CoordStack& getCoordStackSingleton();
+
+	void ResetNewtonianGravity(GravityInput newGravIn, GravityOutput newGravOut);
+	void DispatchNewtonianGravity();
+	void UpdateGravityMask();
 };
diff --git a/src/simulation/gravity/Fft.cpp b/src/simulation/gravity/Fft.cpp
index 43757263f..5cec0295a 100644
--- a/src/simulation/gravity/Fft.cpp
+++ b/src/simulation/gravity/Fft.cpp
@@ -204,7 +204,7 @@ void GravityImpl::Init()
 	});
 }
 
-void Gravity::Exchange(GravityOutput &gravOut, const GravityInput &gravIn)
+void Gravity::Exchange(GravityOutput &gravOut, GravityInput &gravIn)
 {
 	auto *fftGravity = static_cast<GravityImpl *>(this);
 
@@ -231,7 +231,7 @@ void Gravity::Exchange(GravityOutput &gravOut, const GravityInput &gravIn)
 	    std::memcmp(&fftGravity->gravIn.mask[{ 0, 0 }], &gravIn.mask[{ 0, 0 }], NCELL * sizeof(float)))
 	{
 		fftGravity->copyGravOut = true;
-		fftGravity->gravIn = gravIn;
+		std::swap(gravIn, fftGravity->gravIn);
 	}
 
 	fftGravity->Dispatch();
diff --git a/src/simulation/gravity/Gravity.h b/src/simulation/gravity/Gravity.h
index cab143200..da14c0f5a 100644
--- a/src/simulation/gravity/Gravity.h
+++ b/src/simulation/gravity/Gravity.h
@@ -8,7 +8,8 @@ protected:
 	Gravity() = default;
 
 public:
-	void Exchange(GravityOutput &gravOut, const GravityInput &gravIn);
+	// potentially clobbers gravIn
+	void Exchange(GravityOutput &gravOut, GravityInput &gravIn);
 
 	static GravityPtr Create();
 };
diff --git a/src/simulation/gravity/Null.cpp b/src/simulation/gravity/Null.cpp
index c57b8d057..772f02560 100644
--- a/src/simulation/gravity/Null.cpp
+++ b/src/simulation/gravity/Null.cpp
@@ -1,6 +1,6 @@
 #include "Gravity.h"
 
-void Gravity::Exchange(GravityOutput &gravOut, const GravityInput &gravIn)
+void Gravity::Exchange(GravityOutput &gravOut, GravityInput &gravIn)
 {
 }