diff --git a/lib/spdylay_map.c b/lib/spdylay_map.c
index eaa6a42..842eef1 100644
--- a/lib/spdylay_map.c
+++ b/lib/spdylay_map.c
@@ -24,11 +24,10 @@
  */
 #include "spdylay_map.h"
 
-int spdylay_map_init(spdylay_map *map)
+void spdylay_map_init(spdylay_map *map)
 {
   map->root = NULL;
   map->size = 0;
-  return 0;
 }
 
 static void spdylay_map_entry_free(spdylay_map_entry *entry)
diff --git a/lib/spdylay_map.h b/lib/spdylay_map.h
index d78b2cd..780a620 100644
--- a/lib/spdylay_map.h
+++ b/lib/spdylay_map.h
@@ -49,18 +49,59 @@ typedef struct {
   size_t size;
 } spdylay_map;
 
-int spdylay_map_init(spdylay_map *map);
+/*
+ * Initializes the map |map|.
+ */
+void spdylay_map_init(spdylay_map *map);
 
+/*
+ * Deallocates any resources allocated for |map|. The stored items are
+ * not freed by this function. Use spdylay_map_each() to free each
+ * item.
+ */
 void spdylay_map_free(spdylay_map *map);
 
+/*
+ * Inserts the new item |val| with the key |key| to the map |map|.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error code:
+ *
+ * SPDYLAY_ERR_INVALID_ARGUMENT
+ *     The item associated by |key| already exists.
+ *
+ * SPDYLAY_ERR_NOMEM
+ *     Out of memory.
+ */
 int spdylay_map_insert(spdylay_map *map, key_type key, void *val);
 
+/*
+ * Returns the item associated by the key |key|.  If there is no such
+ * item, this function returns NULL.
+ */
 void* spdylay_map_find(spdylay_map *map, key_type key);
 
+/*
+ * Erases the item associated by the key |key|.  The erased item is
+ * not freed by this function.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * SPDYLAY_ERR_INVALID_ARGUMENT
+ *     The item associated by |key| does not exist.
+ */
 void spdylay_map_erase(spdylay_map *map, key_type key);
 
+/*
+ * Returns the number of items stored in the map |map|.
+ */
 size_t spdylay_map_size(spdylay_map *map);
 
+/*
+ * Applies the function |func| to each key/item pair in the map |map|.
+ * This function is useful to free item in the map.
+ */
 void spdylay_map_each(spdylay_map *map, void (*func)(key_type key, void *val));
 
 #endif /* SPDYLAY_MAP_H */
diff --git a/lib/spdylay_session.c b/lib/spdylay_session.c
index ec6fcf9..ded051c 100644
--- a/lib/spdylay_session.c
+++ b/lib/spdylay_session.c
@@ -102,10 +102,7 @@ static int spdylay_session_new(spdylay_session **session_ptr,
   if(r != 0) {
     goto fail_hd_inflater;
   }
-  r = spdylay_map_init(&(*session_ptr)->streams);
-  if(r != 0) {
-    goto fail_streams;
-  }
+  spdylay_map_init(&(*session_ptr)->streams);
   r = spdylay_pq_init(&(*session_ptr)->ob_pq, spdylay_outbound_item_compar);
   if(r != 0) {
     goto fail_ob_pq;
@@ -159,7 +156,6 @@ static int spdylay_session_new(spdylay_session **session_ptr,
   spdylay_pq_free(&(*session_ptr)->ob_pq);
  fail_ob_pq:
   spdylay_map_free(&(*session_ptr)->streams);
- fail_streams:
   spdylay_zlib_inflate_free(&(*session_ptr)->hd_inflater);
  fail_hd_inflater:
   spdylay_zlib_deflate_free(&(*session_ptr)->hd_deflater);
diff --git a/tests/spdylay_map_test.c b/tests/spdylay_map_test.c
index af3a046..99b2cb9 100644
--- a/tests/spdylay_map_test.c
+++ b/tests/spdylay_map_test.c
@@ -31,7 +31,7 @@
 void test_spdylay_map()
 {
   spdylay_map map;
-  CU_ASSERT(0 == spdylay_map_init(&map));
+  spdylay_map_init(&map);
   CU_ASSERT(0 == spdylay_map_insert(&map, 1, "foo"));
   CU_ASSERT(strcmp("foo", spdylay_map_find(&map, 1)) == 0);
   CU_ASSERT(1 == spdylay_map_size(&map));