diff --git a/src/java/org/apache/cassandra/io/sstable/format/SSTableReader.java b/src/java/org/apache/cassandra/io/sstable/format/SSTableReader.java
index f046991878..92359e4d0c 100644
--- a/src/java/org/apache/cassandra/io/sstable/format/SSTableReader.java
+++ b/src/java/org/apache/cassandra/io/sstable/format/SSTableReader.java
@@ -179,7 +179,7 @@ public abstract class SSTableReader extends SSTable implements UnfilteredSource,
     public static final Comparator<SSTableReader> maxTimestampAscending = Comparator.comparingLong(SSTableReader::getMaxTimestamp);
     public static final Comparator<SSTableReader> maxTimestampDescending = maxTimestampAscending.reversed();
 
-    private static final TimeUUID.Generator.Factory<UniqueIdentifier> UNIQUE_IDENTIFIER_FACTORY = new TimeUUID.Generator.Factory<UniqueIdentifier>()
+    public static final TimeUUID.Generator.Factory<UniqueIdentifier> UNIQUE_IDENTIFIER_FACTORY = new TimeUUID.Generator.Factory<UniqueIdentifier>()
     {
         @Override
         public UniqueIdentifier atUnixMicrosWithLsb(long unixMicros, long clockSeqAndNode)
@@ -197,6 +197,7 @@ public abstract class SSTableReader extends SSTable implements UnfilteredSource,
             super(unixMicros, clockSeqAndNode);
         }
     }
+
     public final UniqueIdentifier instanceId = TimeUUID.Generator.nextTimeUUID(UNIQUE_IDENTIFIER_FACTORY);
 
     public static final Comparator<SSTableReader> firstKeyComparator = (o1, o2) -> o1.getFirst().compareTo(o2.getFirst());
@@ -1868,11 +1869,17 @@ public abstract class SSTableReader extends SSTable implements UnfilteredSource,
                                           boolean isOffline,
                                           IVerifier.Options options);
 
+    public UniqueIdentifier instanceId()
+    {
+        return instanceId;
+    }
+
     @Override
     public int compareTo(SSTableReader other)
     {
         // Used in IntervalTree with the expecation that compareTo uniquely identifies an SSTableReader
-        return instanceId.compareTo(other.instanceId);
+        // Use accessor for instanceId for mocks
+        return instanceId().compareTo(other.instanceId());
     }
 
     /**
diff --git a/test/unit/org/apache/cassandra/db/compaction/UnifiedCompactionStrategyTest.java b/test/unit/org/apache/cassandra/db/compaction/UnifiedCompactionStrategyTest.java
index 78121d7d78..422d67e946 100644
--- a/test/unit/org/apache/cassandra/db/compaction/UnifiedCompactionStrategyTest.java
+++ b/test/unit/org/apache/cassandra/db/compaction/UnifiedCompactionStrategyTest.java
@@ -66,12 +66,14 @@ import org.apache.cassandra.utils.FBUtilities;
 import org.apache.cassandra.utils.Interval;
 import org.apache.cassandra.utils.Overlaps;
 import org.apache.cassandra.utils.Pair;
+import org.apache.cassandra.utils.TimeUUID;
 import org.apache.cassandra.utils.concurrent.Transactional;
 import org.mockito.Answers;
 import org.mockito.Mock;
 import org.mockito.Mockito;
 import org.mockito.MockitoAnnotations;
 
+import static org.apache.cassandra.io.sstable.format.SSTableReader.UNIQUE_IDENTIFIER_FACTORY;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
@@ -1053,6 +1055,8 @@ public class UnifiedCompactionStrategyTest
         when(ret.getFirst()).thenReturn(first);
         when(ret.getLast()).thenReturn(last);
         when(ret.getInterval()).thenReturn(new Interval<>(first, last, ret));
+        when(ret.instanceId()).thenReturn(TimeUUID.Generator.nextTimeUUID(UNIQUE_IDENTIFIER_FACTORY));
+        when(ret.compareTo(any())).thenCallRealMethod();
         when(ret.isMarkedSuspect()).thenReturn(false);
         when(ret.isRepaired()).thenReturn(false);
         when(ret.getRepairedAt()).thenReturn(repairedAt);