diff --git a/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/planner/CachedSet.h b/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/planner/CachedSet.h
index afa02cd..c5d03a7 100644
--- a/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/planner/CachedSet.h
+++ b/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/planner/CachedSet.h
@@ -108,7 +108,7 @@
 private:
     CachedSet() = default;
 
-    NonBufferHash mFingerprint = 0;
+    const NonBufferHash mFingerprint;
     std::chrono::steady_clock::time_point mLastUpdate = std::chrono::steady_clock::now();
     std::vector<Layer> mLayers;
     Rect mBounds = Rect::EMPTY_RECT;
diff --git a/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/planner/Flattener.h b/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/planner/Flattener.h
index 313a180..2f2ad4c 100644
--- a/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/planner/Flattener.h
+++ b/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/planner/Flattener.h
@@ -54,7 +54,7 @@
 
     void resetActivities(NonBufferHash, std::chrono::steady_clock::time_point now);
 
-    void updateLayersHash();
+    NonBufferHash computeLayersHash() const;
 
     bool mergeWithCachedSets(const std::vector<const LayerState*>& layers,
                              std::chrono::steady_clock::time_point now);
@@ -69,7 +69,6 @@
     std::chrono::steady_clock::time_point mLastGeometryUpdate;
 
     std::vector<CachedSet> mLayers;
-    NonBufferHash mLayersHash = 0;
     std::optional<CachedSet> mNewCachedSet;
 
     // Statistics
diff --git a/services/surfaceflinger/CompositionEngine/src/planner/Flattener.cpp b/services/surfaceflinger/CompositionEngine/src/planner/Flattener.cpp
index ffca5ba..9c9649c 100644
--- a/services/surfaceflinger/CompositionEngine/src/planner/Flattener.cpp
+++ b/services/surfaceflinger/CompositionEngine/src/planner/Flattener.cpp
@@ -40,13 +40,17 @@
 
     ++mInitialLayerCounts[layers.size()];
 
-    if (mergeWithCachedSets(layers, now)) {
-        hash = mLayersHash;
-    }
+    // Only buildCachedSets if these layers are already stored in mLayers.
+    // Otherwise (i.e. mergeWithCachedSets returns false), the time has not
+    // changed, so buildCachedSets will never find any runs.
+    const bool alreadyHadCachedSets = mergeWithCachedSets(layers, now);
 
     ++mFinalLayerCounts[mLayers.size()];
 
-    buildCachedSets(now);
+    if (alreadyHadCachedSets) {
+        buildCachedSets(now);
+        hash = computeLayersHash();
+    }
 
     return hash;
 }
@@ -157,14 +161,17 @@
     }
 }
 
-void Flattener::updateLayersHash() {
+NonBufferHash Flattener::computeLayersHash() const{
     size_t hash = 0;
     for (const auto& layer : mLayers) {
         android::hashCombineSingleHashed(hash, layer.getNonBufferHash());
     }
-    mLayersHash = hash;
+    return hash;
 }
 
+// Only called if the geometry matches the last frame. Return true if mLayers
+// was already populated with these layers, i.e. on the second and following
+// calls with the same geometry.
 bool Flattener::mergeWithCachedSets(const std::vector<const LayerState*>& layers, time_point now) {
     std::vector<CachedSet> merged;
 
@@ -272,7 +279,6 @@
     }
 
     mLayers = std::move(merged);
-    updateLayersHash();
     return true;
 }