diff --git a/lib/nghttp2_frame.c b/lib/nghttp2_frame.c
index 734528ae..adb05650 100644
--- a/lib/nghttp2_frame.c
+++ b/lib/nghttp2_frame.c
@@ -181,17 +181,17 @@ void nghttp2_frame_window_update_init(nghttp2_window_update *frame,
 void nghttp2_frame_window_update_free(nghttp2_window_update *frame)
 {}
 
-void nghttp2_frame_data_init(nghttp2_data *frame, uint8_t flags,
+void nghttp2_frame_data_init(nghttp2_private_data *frame, uint8_t flags,
                              int32_t stream_id,
                              const nghttp2_data_provider *data_prd)
 {
-  memset(frame, 0, sizeof(nghttp2_data));
+  memset(frame, 0, sizeof(nghttp2_private_data));
   /* At this moment, the length of DATA frame is unknown */
   nghttp2_frame_set_hd(&frame->hd, 0, NGHTTP2_DATA, flags, stream_id);
   frame->data_prd = *data_prd;
 }
 
-void nghttp2_frame_data_free(nghttp2_data *frame)
+void nghttp2_frame_data_free(nghttp2_private_data *frame)
 {}
 
 /*
diff --git a/lib/nghttp2_frame.h b/lib/nghttp2_frame.h
index 8b4dfa5f..ec07e373 100644
--- a/lib/nghttp2_frame.h
+++ b/lib/nghttp2_frame.h
@@ -58,7 +58,9 @@ typedef enum {
 
 /**
  * @struct
- * The DATA frame. It has the following members:
+ *
+ * The DATA frame used in the library privately. It has the following
+ * members:
  */
 typedef struct {
   nghttp2_frame_hd hd;
@@ -72,7 +74,7 @@ typedef struct {
    * exclusively by nghttp2 library and not in the spec.
    */
   uint8_t eof;
-} nghttp2_data;
+} nghttp2_private_data;
 
 int nghttp2_frame_is_data_frame(uint8_t *head);
 
@@ -414,11 +416,11 @@ void nghttp2_frame_window_update_init(nghttp2_window_update *frame,
 
 void nghttp2_frame_window_update_free(nghttp2_window_update *frame);
 
-void nghttp2_frame_data_init(nghttp2_data *frame, uint8_t flags,
+void nghttp2_frame_data_init(nghttp2_private_data *frame, uint8_t flags,
                              int32_t stream_id,
                              const nghttp2_data_provider *data_prd);
 
-void nghttp2_frame_data_free(nghttp2_data *frame);
+void nghttp2_frame_data_free(nghttp2_private_data *frame);
 
 /*
  * Makes copy of |iv| and return the copy. The |niv| is the number of
diff --git a/lib/nghttp2_outbound_item.c b/lib/nghttp2_outbound_item.c
index 84d2b659..26782013 100644
--- a/lib/nghttp2_outbound_item.c
+++ b/lib/nghttp2_outbound_item.c
@@ -64,7 +64,7 @@ void nghttp2_outbound_item_free(nghttp2_outbound_item *item)
       break;
     }
   } else if(item->frame_cat == NGHTTP2_CAT_DATA) {
-    nghttp2_data *data_frame;
+    nghttp2_private_data *data_frame;
     data_frame = nghttp2_outbound_item_get_data_frame(item);
     nghttp2_frame_data_free(data_frame);
   } else {
diff --git a/lib/nghttp2_outbound_item.h b/lib/nghttp2_outbound_item.h
index e9e6c00a..d0b53b49 100644
--- a/lib/nghttp2_outbound_item.h
+++ b/lib/nghttp2_outbound_item.h
@@ -47,7 +47,7 @@ typedef struct {
   void *frame;
   void *aux_data;
   /* Type of |frame|. NGHTTP2_CTRL: nghttp2_frame*, NGHTTP2_DATA:
-     nghttp2_data* */
+     nghttp2_private_data* */
   nghttp2_frame_category frame_cat;
   /* The priority used in priority comparion */
   int32_t pri;
@@ -63,6 +63,7 @@ void nghttp2_outbound_item_free(nghttp2_outbound_item *item);
 #define nghttp2_outbound_item_get_ctrl_frame(ITEM) ((nghttp2_frame*)ITEM->frame)
 #define nghttp2_outbound_item_get_ctrl_frame_type(ITEM) \
   (((nghttp2_frame*)ITEM->frame)->hd.type)
-#define nghttp2_outbound_item_get_data_frame(ITEM) ((nghttp2_data*)ITEM->frame)
+#define nghttp2_outbound_item_get_data_frame(ITEM) \
+  ((nghttp2_private_data*)ITEM->frame)
 
 #endif /* NGHTTP2_OUTBOUND_ITEM_H */
diff --git a/lib/nghttp2_session.c b/lib/nghttp2_session.c
index 14b59dd7..da553bd9 100644
--- a/lib/nghttp2_session.c
+++ b/lib/nghttp2_session.c
@@ -420,7 +420,7 @@ static int outbound_item_update_pri
       return 0;
     }
   } else {
-    if(((nghttp2_data*)item->frame)->hd.stream_id != stream->stream_id) {
+    if(((nghttp2_private_data*)item->frame)->hd.stream_id != stream->stream_id) {
       return 0;
     }
   }
@@ -535,7 +535,7 @@ int nghttp2_session_add_frame(nghttp2_session *session,
       r = nghttp2_pq_push(&session->ob_pq, item);
     }
   } else if(frame_cat == NGHTTP2_CAT_DATA) {
-    nghttp2_data *data_frame = (nghttp2_data*)abs_frame;
+    nghttp2_private_data *data_frame = (nghttp2_private_data*)abs_frame;
     nghttp2_stream *stream;
     stream = nghttp2_session_get_stream(session, data_frame->hd.stream_id);
     if(stream) {
@@ -1264,7 +1264,7 @@ static ssize_t nghttp2_session_prep_frame(nghttp2_session *session,
   } else if(item->frame_cat == NGHTTP2_CAT_DATA) {
     size_t next_readmax;
     nghttp2_stream *stream;
-    nghttp2_data *data_frame;
+    nghttp2_private_data *data_frame;
     int r;
     data_frame = nghttp2_outbound_item_get_data_frame(item);
     r = nghttp2_session_predicate_data_send(session, data_frame->hd.stream_id);
@@ -1572,7 +1572,7 @@ static int nghttp2_session_after_frame_sent(nghttp2_session *session)
     nghttp2_active_outbound_item_reset(&session->aob);
   } else if(item->frame_cat == NGHTTP2_CAT_DATA) {
     int r;
-    nghttp2_data *data_frame;
+    nghttp2_private_data *data_frame;
     data_frame = nghttp2_outbound_item_get_data_frame(session->aob.item);
     if(session->callbacks.on_data_send_callback) {
       if(session->callbacks.on_data_send_callback
@@ -1763,7 +1763,7 @@ int nghttp2_session_send(nghttp2_session *session)
     } else {
       if(session->aob.item->frame_cat == NGHTTP2_CAT_DATA &&
          session->aob.framebufoff + sentlen > NGHTTP2_FRAME_HEAD_LENGTH) {
-        nghttp2_data *frame;
+        nghttp2_private_data *frame;
         nghttp2_stream *stream;
         uint16_t len;
         if(session->aob.framebufoff < NGHTTP2_FRAME_HEAD_LENGTH) {
@@ -4029,7 +4029,7 @@ int nghttp2_session_add_settings(nghttp2_session *session, uint8_t flags,
 ssize_t nghttp2_session_pack_data(nghttp2_session *session,
                                   uint8_t **buf_ptr, size_t *buflen_ptr,
                                   size_t datamax,
-                                  nghttp2_data *frame)
+                                  nghttp2_private_data *frame)
 {
   ssize_t framelen = datamax+8, r;
   int eof_flags;
diff --git a/lib/nghttp2_session.h b/lib/nghttp2_session.h
index c5236a13..fab43caa 100644
--- a/lib/nghttp2_session.h
+++ b/lib/nghttp2_session.h
@@ -220,7 +220,7 @@ int nghttp2_session_is_my_stream_id(nghttp2_session *session,
  * |frame_cat| must be either NGHTTP2_CTRL or NGHTTP2_DATA. If the
  * |frame_cat| is NGHTTP2_CTRL, the |frame| must be a pointer to
  * nghttp2_frame. If the |frame_cat| is NGHTTP2_DATA, it must be a
- * pointer to nghttp2_data. |aux_data| is a pointer to the arbitrary
+ * pointer to nghttp2_private_data. |aux_data| is a pointer to the arbitrary
  * data. Its interpretation is defined per the type of the frame. When
  * this function succeeds, it takes ownership of |frame| and
  * |aux_data|, so caller must not free them on success.
@@ -530,7 +530,7 @@ nghttp2_stream* nghttp2_session_get_stream(nghttp2_session *session,
 ssize_t nghttp2_session_pack_data(nghttp2_session *session,
                                   uint8_t **buf_ptr, size_t *buflen_ptr,
                                   size_t datamax,
-                                  nghttp2_data *frame);
+                                  nghttp2_private_data *frame);
 
 /*
  * Returns top of outbound frame queue. This function returns NULL if
diff --git a/lib/nghttp2_submit.c b/lib/nghttp2_submit.c
index ced1a831..e74ec94d 100644
--- a/lib/nghttp2_submit.c
+++ b/lib/nghttp2_submit.c
@@ -301,10 +301,10 @@ int nghttp2_submit_data(nghttp2_session *session, uint8_t flags,
                         const nghttp2_data_provider *data_prd)
 {
   int r;
-  nghttp2_data *data_frame;
+  nghttp2_private_data *data_frame;
   uint8_t nflags = 0;
 
-  data_frame = malloc(sizeof(nghttp2_data));
+  data_frame = malloc(sizeof(nghttp2_private_data));
   if(data_frame == NULL) {
     return NGHTTP2_ERR_NOMEM;
   }
diff --git a/tests/nghttp2_session_test.c b/tests/nghttp2_session_test.c
index 8cd5cc4d..f63d931e 100644
--- a/tests/nghttp2_session_test.c
+++ b/tests/nghttp2_session_test.c
@@ -3576,7 +3576,7 @@ void test_nghttp2_session_data_read_temporal_failure(void)
   my_user_data ud;
   nghttp2_data_provider data_prd;
   nghttp2_frame frame;
-  nghttp2_data *data_frame;
+  nghttp2_private_data *data_frame;
   nghttp2_stream *stream;
   size_t data_size = 128*1024;
 
@@ -3599,7 +3599,7 @@ void test_nghttp2_session_data_read_temporal_failure(void)
   stream = nghttp2_session_get_stream(session, 1);
   CU_ASSERT(NULL != stream->deferred_data);
   CU_ASSERT(NGHTTP2_CAT_DATA == stream->deferred_data->frame_cat);
-  data_frame = (nghttp2_data*)stream->deferred_data->frame;
+  data_frame = (nghttp2_private_data*)stream->deferred_data->frame;
   data_frame->data_prd.read_callback =
     temporal_failure_data_source_read_callback;