diff --git a/library/bignum_mod.h b/library/bignum_mod.h
index 982a9ac..c25eb87 100644
--- a/library/bignum_mod.h
+++ b/library/bignum_mod.h
@@ -1,5 +1,7 @@
 /**
  *  Modular bignum functions
+ *
+ * This module implements operations on integers modulo some fixed modulus.
  */
 
 /*