diff --git a/lib/includes/spdylay/spdylay.h b/lib/includes/spdylay/spdylay.h
index 87815623..6bf60a95 100644
--- a/lib/includes/spdylay/spdylay.h
+++ b/lib/includes/spdylay/spdylay.h
@@ -73,6 +73,8 @@ typedef enum {
   SPDYLAY_PING = 6,
   SPDYLAY_GOAWAY = 7,
   SPDYLAY_HEADERS = 8,
+  /* Since SPDY/3 */
+  SPDYLAY_WINDOW_UPDATE = 9,
   SPDYLAY_DATA = 100,
 } spdylay_frame_type;
 
@@ -143,7 +145,7 @@ typedef struct {
      SPDYLAY_SPDY3_LOWEST_PRI (loweset), depending on the protocol
      version. */
   uint8_t pri;
-  /* Use in spdy/3 only */
+  /* Since SPDY/3 */
   uint8_t slot;
   char **nv;
 } spdylay_syn_stream;
@@ -187,10 +189,17 @@ typedef struct {
 typedef struct {
   spdylay_ctrl_hd hd;
   int32_t last_good_stream_id;
-  /* spdy/3 only */
+  /* Since SPDY/3 */
   uint32_t status_code;
 } spdylay_goaway;
 
+/* WINDOW_UPDATE is introduced since SPDY/3 */
+typedef struct {
+  spdylay_ctrl_hd hd;
+  int32_t stream_id;
+  int32_t delta_window_size;
+} spdylay_window_update;
+
 typedef union {
   int fd;
   void *ptr;
@@ -237,6 +246,8 @@ typedef union {
   spdylay_ping ping;
   spdylay_goaway goaway;
   spdylay_headers headers;
+  /* Since SPDY/3 */
+  spdylay_window_update window_update;
   spdylay_data data;
 } spdylay_frame;
 
diff --git a/lib/spdylay_frame.c b/lib/spdylay_frame.c
index e651d9ba..d29b386f 100644
--- a/lib/spdylay_frame.c
+++ b/lib/spdylay_frame.c
@@ -495,6 +495,23 @@ void spdylay_frame_rst_stream_init(spdylay_rst_stream *frame,
 void spdylay_frame_rst_stream_free(spdylay_rst_stream *frame)
 {}
 
+void spdylay_frame_window_update_init(spdylay_window_update *frame,
+                                      uint16_t version,
+                                      int32_t stream_id,
+                                      int32_t delta_window_size)
+{
+  memset(frame, 0, sizeof(spdylay_window_update));
+  frame->hd.version = version;
+  frame->hd.type = SPDYLAY_WINDOW_UPDATE;
+  frame->hd.flags = 0;
+  frame->hd.length = 8;
+  frame->stream_id = stream_id;
+  frame->delta_window_size = delta_window_size;
+}
+
+void spdylay_frame_window_update_free(spdylay_window_update *frame)
+{}
+
 void spdylay_frame_settings_init(spdylay_settings *frame,
                                  uint16_t version, uint8_t flags,
                                  spdylay_settings_entry *iv, size_t niv)
@@ -823,6 +840,37 @@ int spdylay_frame_unpack_rst_stream(spdylay_rst_stream *frame,
   return 0;
 }
 
+ssize_t spdylay_frame_pack_window_update(uint8_t **buf_ptr, size_t *buflen_ptr,
+                                         spdylay_window_update *frame)
+{
+  ssize_t framelen = 16;
+  int r;
+  r = spdylay_reserve_buffer(buf_ptr, buflen_ptr, framelen);
+  if(r != 0) {
+    return r;
+  }
+  memset(*buf_ptr, 0, framelen);
+  spdylay_frame_pack_ctrl_hd(*buf_ptr, &frame->hd);
+  spdylay_put_uint32be(&(*buf_ptr)[8], frame->stream_id);
+  spdylay_put_uint32be(&(*buf_ptr)[12], frame->delta_window_size);
+  return framelen;
+}
+
+int spdylay_frame_unpack_window_update(spdylay_window_update *frame,
+                                       const uint8_t *head, size_t headlen,
+                                       const uint8_t *payload,
+                                       size_t payloadlen)
+{
+  if(payloadlen != 8) {
+    return SPDYLAY_ERR_INVALID_FRAME;
+  }
+  spdylay_frame_unpack_ctrl_hd(&frame->hd, head);
+  frame->stream_id = spdylay_get_uint32(payload) & SPDYLAY_STREAM_ID_MASK;
+  frame->delta_window_size = spdylay_get_uint32(&payload[4]) &
+    SPDYLAY_DELTA_WINDOW_SIZE_MASK;
+  return 0;
+}
+
 ssize_t spdylay_frame_pack_settings(uint8_t **buf_ptr, size_t *buflen_ptr,
                                     spdylay_settings *frame)
 {
diff --git a/lib/spdylay_frame.h b/lib/spdylay_frame.h
index 07418953..71856a1a 100644
--- a/lib/spdylay_frame.h
+++ b/lib/spdylay_frame.h
@@ -36,6 +36,7 @@
 #define SPDYLAY_STREAM_ID_MASK 0x7fffffff
 #define SPDYLAY_LENGTH_MASK 0xffffff
 #define SPDYLAY_VERSION_MASK 0x7fff
+#define SPDYLAY_DELTA_WINDOW_SIZE_MASK 0x7fffffff
 
 /* The length of DATA frame payload. */
 #define SPDYLAY_DATA_PAYLOAD_LENGTH 4096
@@ -287,7 +288,7 @@ int spdylay_frame_unpack_headers(spdylay_headers *frame,
  * Packs RST_STREAM frame |frame| in wire frame format and store it in
  * |*buf_ptr|. The capacity of |*buf_ptr| is |*buflen_ptr|
  * length. This function expands |*buf_ptr| as necessary to store
- * given |frame|. In spdy/2 spc, RST_STREAM wire format is always 16
+ * given |frame|. In spdy/2 spec, RST_STREAM wire format is always 16
  * bytes long.
  *
  * This function returns the size of packed frame if it succeeds, or
@@ -312,6 +313,37 @@ int spdylay_frame_unpack_rst_stream(spdylay_rst_stream *frame,
                                     const uint8_t *head, size_t headlen,
                                     const uint8_t *payload, size_t payloadlen);
 
+
+/*
+ * Packs WINDOW_UPDATE frame |frame| in wire frame format and store it
+ * in |*buf_ptr|. The capacity of |*buf_ptr| is |*buflen_ptr|
+ * length. This function expands |*buf_ptr| as necessary to store
+ * given |frame|. In SPDY/3 spec, WINDOW_UPDATE wire format is always 16
+ * bytes long.
+ *
+ * This function returns the size of packed frame if it succeeds, or
+ * returns one of the following negative error codes:
+ *
+ * SPDYLAY_ERR_NOMEM
+ *     Out of memory.
+ */
+ssize_t spdylay_frame_pack_window_update(uint8_t **buf_ptr, size_t *buflen_ptr,
+                                         spdylay_window_update *frame);
+
+/*
+ * Unpacks WINDOW_UPDATE frame byte sequence into |frame|.
+ *
+ * This function returns 0 if it succeeds or one of the following
+ * negative error codes:
+ *
+ * SPDYLAY_ERR_INVALID_FRAME
+ *     The input data are invalid.
+ */
+int spdylay_frame_unpack_window_update(spdylay_window_update *frame,
+                                       const uint8_t *head, size_t headlen,
+                                       const uint8_t *payload,
+                                       size_t payloadlen);
+
 /*
  * Packs SETTINGS frame |frame| in wire format and store it in
  * |*buf_ptr|. The capacity of |*buf_ptr| is |*buflen_ptr|
@@ -448,6 +480,13 @@ void spdylay_frame_rst_stream_init(spdylay_rst_stream *frame,
 
 void spdylay_frame_rst_stream_free(spdylay_rst_stream *frame);
 
+void spdylay_frame_window_update_init(spdylay_window_update *frame,
+                                      uint16_t version,
+                                      int32_t stream_id,
+                                      int32_t delta_window_size);
+
+void spdylay_frame_window_update_free(spdylay_window_update *frame);
+
 /*
  * Initializes SETTINGS frame |frame| with given values. |frame| takes
  * ownership of |iv|, so caller must not free it.
diff --git a/tests/main.c b/tests/main.c
index 6786cbaf..e8b4cf9a 100644
--- a/tests/main.c
+++ b/tests/main.c
@@ -145,6 +145,8 @@ int main(int argc, char* argv[])
                    test_spdylay_frame_pack_syn_reply) ||
       !CU_add_test(pSuite, "frame_pack_headers",
                    test_spdylay_frame_pack_headers) ||
+      !CU_add_test(pSuite, "frame_pack_window_update",
+                   test_spdylay_frame_pack_window_update) ||
       !CU_add_test(pSuite, "frame_pack_settings",
                    test_spdylay_frame_pack_settings) ||
       !CU_add_test(pSuite, "frame_nv_sort", test_spdylay_frame_nv_sort) ||
diff --git a/tests/spdylay_frame_test.c b/tests/spdylay_frame_test.c
index 186137ef..62f2d561 100644
--- a/tests/spdylay_frame_test.c
+++ b/tests/spdylay_frame_test.c
@@ -384,6 +384,33 @@ void test_spdylay_frame_pack_headers()
   test_spdylay_frame_pack_headers_with(SPDYLAY_PROTO_SPDY3);
 }
 
+void test_spdylay_frame_pack_window_update()
+{
+  spdylay_frame frame, oframe;
+  uint8_t *buf = NULL;
+  size_t buflen = 0;
+  ssize_t framelen;
+  spdylay_frame_window_update_init(&frame.window_update, SPDYLAY_PROTO_SPDY3,
+                                   1000000007, 4096);
+  framelen = spdylay_frame_pack_window_update(&buf, &buflen,
+                                              &frame.window_update);
+  CU_ASSERT(0 == spdylay_frame_unpack_window_update
+            (&oframe.window_update,
+             &buf[0], SPDYLAY_FRAME_HEAD_LENGTH,
+             &buf[SPDYLAY_FRAME_HEAD_LENGTH],
+             framelen-SPDYLAY_FRAME_HEAD_LENGTH));
+  CU_ASSERT(1000000007 == oframe.window_update.stream_id);
+  CU_ASSERT(4096 == oframe.window_update.delta_window_size);
+  CU_ASSERT(SPDYLAY_PROTO_SPDY3 == oframe.headers.hd.version);
+  CU_ASSERT(SPDYLAY_WINDOW_UPDATE == oframe.headers.hd.type);
+  CU_ASSERT(SPDYLAY_CTRL_FLAG_NONE == oframe.headers.hd.flags);
+  CU_ASSERT(framelen-SPDYLAY_FRAME_HEAD_LENGTH == oframe.ping.hd.length);
+  free(buf);
+  spdylay_frame_window_update_free(&oframe.window_update);
+  spdylay_frame_window_update_free(&frame.window_update);
+}
+
+
 void test_spdylay_frame_pack_settings()
 {
   spdylay_frame frame, oframe;
diff --git a/tests/spdylay_frame_test.h b/tests/spdylay_frame_test.h
index 3c30e5e8..f567a065 100644
--- a/tests/spdylay_frame_test.h
+++ b/tests/spdylay_frame_test.h
@@ -34,6 +34,7 @@ void test_spdylay_frame_pack_goaway();
 void test_spdylay_frame_pack_syn_stream();
 void test_spdylay_frame_pack_syn_reply();
 void test_spdylay_frame_pack_headers();
+void test_spdylay_frame_pack_window_update();
 void test_spdylay_frame_pack_settings();
 void test_spdylay_frame_nv_sort();
 void test_spdylay_frame_nv_downcase();