diff --git a/libcorpus2_whole/io/corpusreader.h b/libcorpus2_whole/io/corpusreader.h
index dafe17b5496f5ee5b099121db6f3cc16f99048ac..4308b3591f640d35d50ab08a9d24f303e908745e 100644
--- a/libcorpus2_whole/io/corpusreader.h
+++ b/libcorpus2_whole/io/corpusreader.h
@@ -12,6 +12,8 @@ class CorpusReader
 {
 public:
 	/**
+	 * Constructor of corpus reader. Here must be set type of the corpus, which
+	 * will be reading.
 	 * @arg corpus_type may be:
 	 *  - document (contains relations)
 	 *  - poliqarp