diff --git a/lucene/codecs/src/java/org/apache/lucene/codecs/memory/MemoryPostingsFormat.java b/lucene/codecs/src/java/org/apache/lucene/codecs/memory/MemoryPostingsFormat.java
index 67a0d92..f77491a 100644
--- a/lucene/codecs/src/java/org/apache/lucene/codecs/memory/MemoryPostingsFormat.java
+++ b/lucene/codecs/src/java/org/apache/lucene/codecs/memory/MemoryPostingsFormat.java
@@ -640,6 +640,7 @@ public final class MemoryPostingsFormat extends PostingsFormat {
 
     private void decodeMetaData() {
       if (!didDecode) {
+        current.output = BytesRef.deepCopyOf(current.output); // NOCOMMIT this could be a root arc of the FST!
         buffer.reset(current.output.bytes, 0, current.output.length);
         docFreq = buffer.readVInt();
         if (field.getIndexOptions() != IndexOptions.DOCS_ONLY) {
diff --git a/lucene/core/src/java/org/apache/lucene/util/fst/FST.java b/lucene/core/src/java/org/apache/lucene/util/fst/FST.java
index d049235..8be7d09 100644
--- a/lucene/core/src/java/org/apache/lucene/util/fst/FST.java
+++ b/lucene/core/src/java/org/apache/lucene/util/fst/FST.java
@@ -171,6 +171,8 @@ public final class FST<T> {
   private final boolean allowArrayArcs;
 
   private Arc<T> cachedRootArcs[];
+  private Arc<T> assertingCachedRootArcs[]; // only set wit assert
+
 
   /** Represents a single arc. */
   public final static class Arc<T> {
@@ -420,11 +422,18 @@ public final class FST<T> {
       return node;
     }
   }
-
+  
   // Caches first 128 labels
   @SuppressWarnings({"rawtypes","unchecked"})
   private void cacheRootArcs() throws IOException {
     cachedRootArcs = (Arc<T>[]) new Arc[0x80];
+    readRootArcs(cachedRootArcs);
+    
+    assert setAssertingRootArcs(cachedRootArcs);
+    assert assertRootArcs();
+  }
+  
+  public void readRootArcs(Arc<T>[] arcs) throws IOException {
     final Arc<T> arc = new Arc<T>();
     getFirstArc(arc);
     final BytesReader in = getBytesReader();
@@ -433,7 +442,7 @@ public final class FST<T> {
       while(true) {
         assert arc.label != END_LABEL;
         if (arc.label < cachedRootArcs.length) {
-          cachedRootArcs[arc.label] = new Arc<T>().copyFrom(arc);
+          arcs[arc.label] = new Arc<T>().copyFrom(arc);
         } else {
           break;
         }
@@ -444,6 +453,38 @@ public final class FST<T> {
       }
     }
   }
+  
+  @SuppressWarnings({"rawtypes","unchecked"})
+  private boolean setAssertingRootArcs(Arc<T>[] arcs) throws IOException {
+    assertingCachedRootArcs = (Arc<T>[]) new Arc[arcs.length];
+    readRootArcs(assertingCachedRootArcs);
+    return true;
+  }
+  
+  private boolean assertRootArcs() {
+    assert cachedRootArcs != null;
+    assert assertingCachedRootArcs != null;
+    for (int i = 0; i < cachedRootArcs.length; i++) {
+      final Arc<T> root = cachedRootArcs[i];
+      final Arc<T> asserting = assertingCachedRootArcs[i];
+      if (root != null) { 
+        assert root.arcIdx == asserting.arcIdx;
+        assert root.bytesPerArc == asserting.bytesPerArc;
+        assert root.flags == asserting.flags;
+        assert root.label == asserting.label;
+        assert root.nextArc == asserting.nextArc;
+        assert root.nextFinalOutput.equals(asserting.nextFinalOutput);
+        assert root.node == asserting.node;
+        assert root.numArcs == asserting.numArcs;
+        assert root.output.equals(asserting.output);
+        assert root.posArcsStart == asserting.posArcsStart;
+        assert root.target == asserting.target;
+      } else {
+        assert root == null && asserting == null;
+      } 
+    }
+    return true;
+  }
 
   public T getEmptyOutput() {
     return emptyOutput;
@@ -1099,7 +1140,7 @@ public final class FST<T> {
   /** Finds an arc leaving the incoming arc, replacing the arc in place.
    *  This returns null if the arc was not found, else the incoming arc. */
   public Arc<T> findTargetArc(int labelToMatch, Arc<T> follow, Arc<T> arc, BytesReader in) throws IOException {
-    assert cachedRootArcs != null;
+    assert assertRootArcs();
 
     if (labelToMatch == END_LABEL) {
       if (follow.isFinal()) {