diff --git a/cmds/statsd/src/anomaly/AnomalyTracker.cpp b/cmds/statsd/src/anomaly/AnomalyTracker.cpp
index 6ee51f38dde87..133f33b15405e 100644
--- a/cmds/statsd/src/anomaly/AnomalyTracker.cpp
+++ b/cmds/statsd/src/anomaly/AnomalyTracker.cpp
@@ -59,6 +59,12 @@ void AnomalyTracker::resetStorage() {
 }
 
 size_t AnomalyTracker::index(int64_t bucketNum) const {
+    if (bucketNum < 0) {
+        // To support this use-case, we can easily modify index to wrap around. But currently
+        // AnomalyTracker should never need this, so if it happens, it's a bug we should log.
+        // TODO: Audit this.
+        ALOGE("index() was passed a negative bucket number (%lld)!", (long long)bucketNum);
+    }
     return bucketNum % mNumOfPastBuckets;
 }
 
@@ -72,9 +78,7 @@ void AnomalyTracker::flushPastBuckets(const int64_t& latestPastBucketNum) {
     // The past packets are ancient. Empty out old mPastBuckets[i] values and reset
     // mSumOverPastBuckets.
     if (latestPastBucketNum - mMostRecentBucketNum >= mNumOfPastBuckets) {
-        mPastBuckets.clear();
-        mPastBuckets.resize(mNumOfPastBuckets);
-        mSumOverPastBuckets.clear();
+        resetStorage();
     } else {
         for (int64_t i = std::max(0LL, (long long)(mMostRecentBucketNum - mNumOfPastBuckets + 1));
              i <= latestPastBucketNum - mNumOfPastBuckets; i++) {
@@ -150,7 +154,7 @@ void AnomalyTracker::addBucketToSum(const shared_ptr<DimToValMap>& bucket) {
 
 int64_t AnomalyTracker::getPastBucketValue(const MetricDimensionKey& key,
                                            const int64_t& bucketNum) const {
-    if (mNumOfPastBuckets == 0) {
+    if (mNumOfPastBuckets == 0 || bucketNum < 0) {
         return 0;
     }
 
diff --git a/cmds/statsd/src/anomaly/AnomalyTracker.h b/cmds/statsd/src/anomaly/AnomalyTracker.h
index e3f493cfe7cf0..d27dee843b22a 100644
--- a/cmds/statsd/src/anomaly/AnomalyTracker.h
+++ b/cmds/statsd/src/anomaly/AnomalyTracker.h
@@ -110,7 +110,7 @@ protected:
 
     // Number of past buckets. One less than the total number of buckets needed
     // for the anomaly detection (since the current bucket is not in the past).
-    int mNumOfPastBuckets;
+    const int mNumOfPastBuckets;
 
     // The existing bucket list.
     std::vector<shared_ptr<DimToValMap>> mPastBuckets;