diff --git a/dGame/dComponents/Physics/ControllablePhysicsComponent.cpp b/dGame/dComponents/Physics/ControllablePhysicsComponent.cpp
index 2e8efcea7..a04ffaa99 100644
--- a/dGame/dComponents/Physics/ControllablePhysicsComponent.cpp
+++ b/dGame/dComponents/Physics/ControllablePhysicsComponent.cpp
@@ -333,8 +333,7 @@ void ControllablePhysicsComponent::RemovePickupRadiusScale(float value) {
 
 void ControllablePhysicsComponent::AddSpeedboost(float value) {
 	m_ActiveSpeedBoosts.push_back(value);
-	m_SpeedBoost = value;
-	SetSpeedMultiplier(value / 500.0f); // 500 being the base speed
+	UpdateSpeedBoost();
 }
 
 void ControllablePhysicsComponent::RemoveSpeedboost(float value) {
@@ -346,16 +345,35 @@ void ControllablePhysicsComponent::RemoveSpeedboost(float value) {
 		return;
 	}
 
-	// Recalculate speedboost since we removed one
-	m_SpeedBoost = 500.0f; // Entities without level progression (enemies, pets) go back to the normal multiplier of 1
-	if (m_ActiveSpeedBoosts.empty()) { // no active speed boosts left, so return to base speed
+	UpdateSpeedBoost();
+	Game::entityManager->SerializeEntity(m_Parent);
+}
+
+void ControllablePhysicsComponent::UpdateSpeedBoost() {
+	// The client's rule (LWOControllablePhysComponent::msgAddRunspeedModifier 0x00be0af0, msgRemoveRunSpeedModifier
+	// 0x00be0720): a modifier over 1000 or of exactly the base 500 counts for nothing; with any slow (under 500) the
+	// lowest one is the speed, otherwise the highest boost is
+	constexpr float baseSpeed = 500.0f;
+	constexpr float maxModifier = 1000.0f;
+	float lowestSlow = baseSpeed;
+	float highestBoost = baseSpeed;
+	for (const auto boost : m_ActiveSpeedBoosts) {
+		if (boost > maxModifier) continue;
+		if (boost < lowestSlow) lowestSlow = boost;
+		if (boost > highestBoost) highestBoost = boost;
+	}
+
+	if (lowestSlow < baseSpeed) {
+		m_SpeedBoost = lowestSlow;
+	} else if (highestBoost > baseSpeed) {
+		m_SpeedBoost = highestBoost;
+	} else {
+		// No modifier counts: entities without level progression (enemies, pets) go back to the normal multiplier of 1
+		m_SpeedBoost = baseSpeed;
 		auto* levelProgressionComponent = m_Parent->GetComponent<LevelProgressionComponent>();
 		if (levelProgressionComponent) m_SpeedBoost = levelProgressionComponent->GetSpeedBase();
-	} else { // Used the last applied speedboost
-		m_SpeedBoost = m_ActiveSpeedBoosts.back();
 	}
-	SetSpeedMultiplier(m_SpeedBoost / 500.0f); // 500 being the base speed
-	Game::entityManager->SerializeEntity(m_Parent);
+	SetSpeedMultiplier(m_SpeedBoost / baseSpeed);
 }
 
 void ControllablePhysicsComponent::ActivateBubbleBuff(eBubbleType bubbleType, bool specialAnims) {
diff --git a/dGame/dComponents/Physics/ControllablePhysicsComponent.h b/dGame/dComponents/Physics/ControllablePhysicsComponent.h
index 5d5e8e78d..27765cdc5 100644
--- a/dGame/dComponents/Physics/ControllablePhysicsComponent.h
+++ b/dGame/dComponents/Physics/ControllablePhysicsComponent.h
@@ -395,6 +395,11 @@ private:
 	 */
 	bool m_IsTeleporting;
 
+	/**
+	 * Works the speed out of the active speed boosts: the lowest slow if there is one, otherwise the highest boost
+	 */
+	void UpdateSpeedBoost();
+
 	/**
 	 * The list of speed boosts for this entity
 	 */
diff --git a/tests/dGameTests/dComponentsTests/ReplicaConstructionTests.cpp b/tests/dGameTests/dComponentsTests/ReplicaConstructionTests.cpp
index 9d8846b9e..9fec20670 100644
--- a/tests/dGameTests/dComponentsTests/ReplicaConstructionTests.cpp
+++ b/tests/dGameTests/dComponentsTests/ReplicaConstructionTests.cpp
@@ -432,6 +432,40 @@ TEST_F(ReplicaConstructionTest, CharacterGuildChangeIsWrittenOnce) {
 	player.SetCharacter(nullptr);
 }
 
+// Run speed modifiers stack as in LWOControllablePhysComponent::msgAddRunspeedModifier (0x00be0af0) and
+// msgRemoveRunSpeedModifier (0x00be0720): the lowest slow wins, otherwise the highest boost; 500 and anything over 1000
+// count for nothing
+TEST_F(ReplicaConstructionTest, RunSpeedModifiersStackAsTheClientDoes) {
+	Entity entity(15, info);
+	auto* const physics = entity.AddComponent<ControllablePhysicsComponent>(-1);
+	EXPECT_FLOAT_EQ(physics->GetSpeedMultiplier(), 1.0f);
+
+	physics->AddSpeedboost(750.0f);
+	EXPECT_FLOAT_EQ(physics->GetSpeedMultiplier(), 1.5f);
+	physics->AddSpeedboost(550.0f); // a smaller boost applied later does not replace the bigger one
+	EXPECT_FLOAT_EQ(physics->GetSpeedMultiplier(), 1.5f);
+	physics->AddSpeedboost(250.0f); // any slow beats every boost
+	EXPECT_FLOAT_EQ(physics->GetSpeedMultiplier(), 0.5f);
+	physics->AddSpeedboost(133.0f);
+	EXPECT_FLOAT_EQ(physics->GetSpeedMultiplier(), 133.0f / 500.0f);
+	physics->AddSpeedboost(350.0f);
+	EXPECT_FLOAT_EQ(physics->GetSpeedMultiplier(), 133.0f / 500.0f);
+	physics->AddSpeedboost(1500.0f);
+	physics->AddSpeedboost(500.0f);
+	EXPECT_FLOAT_EQ(physics->GetSpeedMultiplier(), 133.0f / 500.0f);
+
+	physics->RemoveSpeedboost(133.0f);
+	EXPECT_FLOAT_EQ(physics->GetSpeedMultiplier(), 0.5f);
+	physics->RemoveSpeedboost(250.0f);
+	EXPECT_FLOAT_EQ(physics->GetSpeedMultiplier(), 0.7f);
+	physics->RemoveSpeedboost(350.0f);
+	EXPECT_FLOAT_EQ(physics->GetSpeedMultiplier(), 1.5f);
+	physics->RemoveSpeedboost(750.0f);
+	EXPECT_FLOAT_EQ(physics->GetSpeedMultiplier(), 1.1f);
+	physics->RemoveSpeedboost(550.0f);
+	EXPECT_FLOAT_EQ(physics->GetSpeedMultiplier(), 1.0f); // 1500 and 500 are left and count for nothing
+}
+
 // Live wrote the cheat block (gravity scale, speed multiplier) on construction only when one of them was changed: 216
 // of 20,617 controllable-physics constructions had it (players at run speed 1.05, enemies with gravity 0), never 1/1.
 TEST_F(ReplicaConstructionTest, ControllablePhysicsConstructionWritesCheatsOnlyWhenChanged) {