diff --git a/tools/h5repack/h5repack_main.c b/tools/h5repack/h5repack_main.c
index 8fd2046e64..f55bd2e530 100644
--- a/tools/h5repack/h5repack_main.c
+++ b/tools/h5repack/h5repack_main.c
@@ -183,7 +183,7 @@ static void usage(const char *prog)
 
  printf("\n");
 
- printf("  M - is an integer greater than 1, size of dataset in bytes \n");
+ printf("  M - is an integer greater than 1, size of dataset in bytes (default is 1024) \n");
  printf("  E - is a filename.\n");
  printf("  S - is an integer\n");
  printf("  U - is a filename.\n");