diff --git a/dynamometer-blockgen/src/main/java/com/linkedin/dynamometer/blockgenerator/XMLParser.java b/dynamometer-blockgen/src/main/java/com/linkedin/dynamometer/blockgenerator/XMLParser.java
index 3b915c23b2..9c26f15048 100644
--- a/dynamometer-blockgen/src/main/java/com/linkedin/dynamometer/blockgenerator/XMLParser.java
+++ b/dynamometer-blockgen/src/main/java/com/linkedin/dynamometer/blockgenerator/XMLParser.java
@@ -38,8 +38,9 @@
  */
 class XMLParser {
 
+  // Legacy block IDs can be negative
   private static final Pattern BLOCK_PATTERN =
-      Pattern.compile("<block><id>(\\d+)</id><genstamp>(\\d+)</genstamp><numBytes>(\\d+)</numBytes></block>");
+      Pattern.compile("<block><id>(-?\\d+)</id><genstamp>(\\d+)</genstamp><numBytes>(\\d+)</numBytes></block>");
 
   private State currentState = State.DEFAULT;
   private short currentReplication;
diff --git a/dynamometer-infra/src/main/java/com/linkedin/dynamometer/SimulatedMultiStorageFSDataset.java b/dynamometer-infra/src/main/java/com/linkedin/dynamometer/SimulatedMultiStorageFSDataset.java
index 54cc38bf86..1642740744 100644
--- a/dynamometer-infra/src/main/java/com/linkedin/dynamometer/SimulatedMultiStorageFSDataset.java
+++ b/dynamometer-infra/src/main/java/com/linkedin/dynamometer/SimulatedMultiStorageFSDataset.java
@@ -581,14 +581,14 @@ public synchronized void injectBlocks(String bpid,
 
       for (Block b: injectBlocks) {
         BInfo binfo = new BInfo(bpid, b, false);
-        blockMaps.get((int) (b.getBlockId() % storages.size())).put(binfo.theBlock, binfo);
+        blockMaps.get((int) Math.floorMod(b.getBlockId(), storages.size())).put(binfo.theBlock, binfo);
       }
     }
   }
 
   /** Get the storage that a given block lives within. */
   private SimulatedStorage getStorage(Block b) {
-    return storages.get((int) (b.getBlockId() % storages.size()));
+    return storages.get((int) Math.floorMod(b.getBlockId(), storages.size()));
   }
 
   /**