diff --git a/packages/SystemUI/src/com/android/systemui/util/animation/PhysicsAnimator.kt b/packages/SystemUI/src/com/android/systemui/util/animation/PhysicsAnimator.kt
index f4157f21e1583..8625d63a3c7ef 100644
--- a/packages/SystemUI/src/com/android/systemui/util/animation/PhysicsAnimator.kt
+++ b/packages/SystemUI/src/com/android/systemui/util/animation/PhysicsAnimator.kt
@@ -125,6 +125,13 @@ class PhysicsAnimator<T> private constructor (val target: T) {
      */
     internal var startAction: () -> Unit = ::startInternal
 
+    /**
+     * Action to run when [cancel] is called. This can be changed by
+     * [PhysicsAnimatorTestUtils.prepareForTest] to cancel animations from the main thread, which
+     * is required.
+     */
+    internal var cancelAction: (Set<FloatPropertyCompat<in T>>) -> Unit = ::cancelInternal
+
     /**
      * Springs a property to the given value, using the provided configuration settings.
      *
@@ -429,10 +436,13 @@ class PhysicsAnimator<T> private constructor (val target: T) {
                         max = max(currentValue, this.max)
                     }
 
-                    // Apply the configuration and start the animation. Since flings can't be
-                    // redirected while in motion, cancel it first.
+                    // Flings can't be updated to a new position while maintaining velocity, because
+                    // we're using the explicitly provided start velocity. Cancel any flings (or
+                    // springs) on this property before flinging.
+                    cancel(animatedProperty)
+
+                    // Apply the configuration and start the animation.
                     getFlingAnimation(animatedProperty)
-                            .also { it.cancel() }
                             .also { flingConfig.applyToAnimation(it) }
                             .start()
                 }
@@ -707,11 +717,26 @@ class PhysicsAnimator<T> private constructor (val target: T) {
         return springConfigs.keys.union(flingConfigs.keys)
     }
 
+    /**
+     * Cancels the given properties. This is typically called immediately by [cancel], unless this
+     * animator is under test.
+     */
+    internal fun cancelInternal(properties: Set<FloatPropertyCompat<in T>>) {
+        for (property in properties) {
+            flingAnimations[property]?.cancel()
+            springAnimations[property]?.cancel()
+        }
+    }
+
     /** Cancels all in progress animations on all properties. */
     fun cancel() {
-        for (dynamicAnim in flingAnimations.values.union(springAnimations.values)) {
-            dynamicAnim.cancel()
-        }
+        cancelAction(flingAnimations.keys)
+        cancelAction(springAnimations.keys)
+    }
+
+    /** Cancels in progress animations on the provided properties only. */
+    fun cancel(vararg properties: FloatPropertyCompat<in T>) {
+        cancelAction(properties.toSet())
     }
 
     /**
diff --git a/packages/SystemUI/src/com/android/systemui/util/animation/PhysicsAnimatorTestUtils.kt b/packages/SystemUI/src/com/android/systemui/util/animation/PhysicsAnimatorTestUtils.kt
index 965decd255a03..c50eeac80d7a9 100644
--- a/packages/SystemUI/src/com/android/systemui/util/animation/PhysicsAnimatorTestUtils.kt
+++ b/packages/SystemUI/src/com/android/systemui/util/animation/PhysicsAnimatorTestUtils.kt
@@ -363,8 +363,12 @@ object PhysicsAnimatorTestUtils {
         private val testEndListeners = ArrayList<PhysicsAnimator.EndListener<T>>()
         private val testUpdateListeners = ArrayList<PhysicsAnimator.UpdateListener<T>>()
 
+        /** Whether we're currently in the middle of executing startInternal(). */
+        private var currentlyRunningStartInternal = false
+
         init {
             animator.startAction = ::startForTest
+            animator.cancelAction = ::cancelForTest
         }
 
         internal fun addTestEndListener(listener: PhysicsAnimator.EndListener<T>) {
@@ -437,7 +441,29 @@ object PhysicsAnimatorTestUtils {
                     }
                 })
 
+                currentlyRunningStartInternal = true
                 animator.startInternal()
+                currentlyRunningStartInternal = false
+                unblockLatch.countDown()
+            }
+
+            unblockLatch.await(timeoutMs, TimeUnit.MILLISECONDS)
+        }
+
+        private fun cancelForTest(properties: Set<FloatPropertyCompat<in T>>) {
+            // If this was called from startInternal, we are already on the animation thread, and
+            // should just call cancelInternal rather than posting it. If we post it, the
+            // cancellation will occur after the rest of startInternal() and we'll immediately
+            // cancel the animation we worked so hard to start!
+            if (currentlyRunningStartInternal) {
+                animator.cancelInternal(properties)
+                return
+            }
+
+            val unblockLatch = CountDownLatch(1)
+
+            animationThreadHandler.post {
+                animator.cancelInternal(properties)
                 unblockLatch.countDown()
             }