diff --git a/bubble.go b/bubble.go
index 12f9280..53286f7 100644
--- a/bubble.go
+++ b/bubble.go
@@ -64,7 +64,7 @@ func (s *Simulator) applyBubbleColumns(state *MovementState) {
 }
 
 func (s *Simulator) attemptRiptide(state *MovementState, touchingWater bool) bool {
-	if s.Equipment == nil || state.RiptideTicks > 0 || !state.RiptideReady || (!touchingWater && !state.RiptideInRain) {
+	if s.Equipment == nil || state.InVehicle || state.RiptideTicks > 0 || !state.RiptideReady || (!touchingWater && !state.RiptideInRain) {
 		return false
 	}
 	level := s.Equipment.EnchantmentLevel(EnchantmentRiptide)
diff --git a/bubble_test.go b/bubble_test.go
index b057f22..a2b72b1 100644
--- a/bubble_test.go
+++ b/bubble_test.go
@@ -125,6 +125,22 @@ func TestRiptideDoesNotLaunchWhileFlying(t *testing.T) {
 	}
 }
 
+func TestRiptideDoesNotLaunchWhileMounted(t *testing.T) {
+	w := environmentWorld{blocks: map[cube.Pos]world.Block{{0, 0, 0}: block.Water{Still: true, Depth: 8}}}
+	sim := &Simulator{World: w, Equipment: fixedEquipment{EnchantmentRiptide: 2}}
+	state := newBaseState()
+	state.Pos = mgl32.Vec3{0.5, 0, 0.5}
+	state.Gravity = NormalGravity
+	state.InVehicle = true
+	state.RiptideReady = true
+
+	sim.Simulate(state, InputState{StartSpinAttack: true})
+
+	if state.RiptideTicks != 0 {
+		t.Fatalf("expected mounted player not to start riptide, got %d ticks", state.RiptideTicks)
+	}
+}
+
 func TestRiptideRequiresValidatedTridentRelease(t *testing.T) {
 	w := environmentWorld{blocks: map[cube.Pos]world.Block{{0, 0, 0}: block.Water{Still: true, Depth: 8}}}
 	sim := &Simulator{World: w, Equipment: fixedEquipment{EnchantmentRiptide: 2}}
diff --git a/movement.go b/movement.go
index 779ffa6..1237a82 100644
--- a/movement.go
+++ b/movement.go
@@ -114,6 +114,9 @@ type MovementState struct {
 	// RiptideInRain is server-observed weather exposure that permits a
 	// validated Riptide release without direct block-water contact.
 	RiptideInRain bool
+	// InVehicle is server-authoritative mounted state. Riptide cannot start
+	// while the player is riding a vehicle.
+	InVehicle bool
 
 	Flying, MayFly, TrustFlyStatus bool
 	JustDisabledFlight             bool