diff --git a/lucene/core/src/java/org/apache/lucene/util/RollingBuffer.java b/lucene/core/src/java/org/apache/lucene/util/RollingBuffer.java
index aad95b68dcf..88d2361bf17 100644
--- a/lucene/core/src/java/org/apache/lucene/util/RollingBuffer.java
+++ b/lucene/core/src/java/org/apache/lucene/util/RollingBuffer.java
@@ -102,7 +102,7 @@ public abstract class RollingBuffer<T extends RollingBuffer.Resettable> {
       nextPos++;
       count++;
     }
-    assert inBounds(pos);
+    assert inBounds(pos): "pos=" + pos + " nextPos=" + nextPos + " count=" + count;
     final int index = getIndex(pos);
     //System.out.println("  pos=" + pos + " nextPos=" + nextPos + " -> index=" + index);
     //assert buffer[index].pos == pos;
@@ -110,11 +110,16 @@ public abstract class RollingBuffer<T extends RollingBuffer.Resettable> {
   }
 
   /** Returns the maximum position looked up, or -1 if no
-  *  position has been looked up sinc reset/init.  */
+  *   position has been looked up since reset/init.  */
   public int getMaxPos() {
     return nextPos-1;
   }
 
+  /** Returns how many active positions are in the buffer. */
+  public int getBufferSize() {
+    return count;
+  }
+
   public void freeBefore(int pos) {
     final int toFree = count - (nextPos - pos);
     assert toFree >= 0;