diff --git a/plugins/org.eclipse.mat.parser/src/org/eclipse/mat/parser/index/IndexWriter.java b/plugins/org.eclipse.mat.parser/src/org/eclipse/mat/parser/index/IndexWriter.java
index 6aca6a0..728e98b 100644
--- a/plugins/org.eclipse.mat.parser/src/org/eclipse/mat/parser/index/IndexWriter.java
+++ b/plugins/org.eclipse.mat.parser/src/org/eclipse/mat/parser/index/IndexWriter.java
@@ -702,6 +702,12 @@
             });
         }
 
+	/**
+	 * Sets a value in the collector.
+	 *
+	 * Safe to be called concurrently from multiple threads. Not safe to mix
+	 * concurrent get and set calls.
+	 */
         public void set(int index, int value)
         {
             ArrayIntCompressed array = getPage(index / pageSize);
@@ -711,6 +717,12 @@
             }
         }
 
+	/**
+	 * Gets from the collected index.
+	 *
+	 * Safe to be called concurrently from multiple threads. Not safe to mix
+	 * concurrent get and set calls.
+	 */
         public int get(int index)
         {
             // set() only happens during parsing stage, get later