diff --git a/src/Particle/HDFWalkerOutput.h b/src/Particle/HDFWalkerOutput.h
index 3d4548862d..57f2ded732 100644
--- a/src/Particle/HDFWalkerOutput.h
+++ b/src/Particle/HDFWalkerOutput.h
@@ -50,7 +50,12 @@ class HDFWalkerOutput
   ~HDFWalkerOutput();
 
   /** dump configurations
-   * @param w walkers
+   * Write walkers into hdf file.
+   * The "walkers" dataset typically resides at "state_0/walkers", which
+   *   contains no information about when it was written (at which block).
+   * The identify_block flag appends the block index to uniquely identify
+   *   each walker dump, e.g., "state_0/walkers10" is from block 10.
+   *
    */
   bool dump(const WalkerConfigurations& w, int block, const bool identify_block=false);
   //     bool dump(ForwardWalkingHistoryObject& FWO);