diff --git a/lib/includes/spdylay/spdylay.h b/lib/includes/spdylay/spdylay.h
index 36074e61..117d48cd 100644
--- a/lib/includes/spdylay/spdylay.h
+++ b/lib/includes/spdylay/spdylay.h
@@ -316,6 +316,14 @@ int spdylay_session_client_new(spdylay_session **session_ptr,
                                const spdylay_session_callbacks *callbacks,
                                void *user_data);
 
+/*
+ * Initializes |*session_ptr| for server use. This function returns 0
+ * if it succeeds, or negative error code.
+ */
+int spdylay_session_server_new(spdylay_session **session_ptr,
+                               const spdylay_session_callbacks *callbacks,
+                               void *user_data);
+
 /*
  * Frees any resources allocated for |session|.
  */
diff --git a/lib/spdylay_session.c b/lib/spdylay_session.c
index 890e8a2a..a8180468 100644
--- a/lib/spdylay_session.c
+++ b/lib/spdylay_session.c
@@ -65,7 +65,7 @@ int spdylay_outbound_item_compar(const void *lhsx, const void *rhsx)
   }
 }
 
-int spdylay_session_client_new(spdylay_session **session_ptr,
+static int spdylay_session_new(spdylay_session **session_ptr,
                                const spdylay_session_callbacks *callbacks,
                                void *user_data)
 {
@@ -76,10 +76,9 @@ int spdylay_session_client_new(spdylay_session **session_ptr,
   }
   memset(*session_ptr, 0, sizeof(spdylay_session));
 
-  /* IDs for use in client */
-  (*session_ptr)->next_stream_id = 1;
-  (*session_ptr)->last_recv_stream_id = 0;
-  (*session_ptr)->next_unique_id = 1;
+  /* next_stream_id, last_recv_stream_id and next_unique_id are
+     initialized in either spdylay_session_client_new or
+     spdylay_session_server_new */
 
   (*session_ptr)->last_ping_unique_id = 0;
 
@@ -124,6 +123,37 @@ int spdylay_session_client_new(spdylay_session **session_ptr,
   return 0;
 }
 
+int spdylay_session_client_new(spdylay_session **session_ptr,
+                               const spdylay_session_callbacks *callbacks,
+                               void *user_data)
+{
+  int r;
+  r = spdylay_session_new(session_ptr, callbacks, user_data);
+  if(r == 0) {
+    /* IDs for use in client */
+    (*session_ptr)->next_stream_id = 1;
+    (*session_ptr)->last_recv_stream_id = 0;
+    (*session_ptr)->next_unique_id = 1;
+  }
+  return r;
+}
+
+int spdylay_session_server_new(spdylay_session **session_ptr,
+                               const spdylay_session_callbacks *callbacks,
+                               void *user_data)
+{
+  int r;
+  r = spdylay_session_new(session_ptr, callbacks, user_data);
+  if(r == 0) {
+    (*session_ptr)->server = 1;
+    /* IDs for use in client */
+    (*session_ptr)->next_stream_id = 2;
+    (*session_ptr)->last_recv_stream_id = 0;
+    (*session_ptr)->next_unique_id = 2;
+  }
+  return r;
+}
+
 static void spdylay_free_streams(key_type key, void *val)
 {
   spdylay_stream_free((spdylay_stream*)val);
@@ -769,13 +799,31 @@ static int spdylay_session_is_new_peer_stream_id(spdylay_session *session,
 static int spdylay_session_validate_syn_stream(spdylay_session *session,
                                                spdylay_syn_stream *frame)
 {
-  /* TODO Check assoc_stream_id */
   if(!spdylay_session_is_new_peer_stream_id(session, frame->stream_id)) {
     return SPDYLAY_PROTOCOL_ERROR;
   }
   if(frame->hd.version != SPDYLAY_PROTO_VERSION) {
     return SPDYLAY_UNSUPPORTED_VERSION;
   }
+  if(session->server) {
+    if(frame->assoc_stream_id != 0) {
+      return SPDYLAY_PROTOCOL_ERROR;
+    }
+  } else {
+    if(frame->assoc_stream_id == 0) {
+      /* spdy/2 spec: When a client receives a SYN_STREAM from the
+         server with an Associated-To-Stream-ID of 0, it must reply with
+         a RST_STREAM with error code INVALID_STREAM. */
+      return SPDYLAY_INVALID_STREAM;
+    }
+    if((frame->hd.flags & SPDYLAY_FLAG_UNIDIRECTIONAL) == 0 ||
+       frame->assoc_stream_id % 2 == 0 ||
+       spdylay_session_get_stream(session, frame->assoc_stream_id) == NULL) {
+      /* It seems spdy/2 spec does not say which status code should be
+         returned in these cases. */
+      return SPDYLAY_PROTOCOL_ERROR;
+    }
+  }
   return 0;
 }
 
diff --git a/lib/spdylay_stream.h b/lib/spdylay_stream.h
index ee4c60aa..f85426c5 100644
--- a/lib/spdylay_stream.h
+++ b/lib/spdylay_stream.h
@@ -77,6 +77,9 @@ typedef struct {
   uint8_t pri;
   /* Bitwise OR of zero or more spdylay_shut_flag values */
   uint8_t shut_flags;
+  /* TODO spdylay_stream should remember pushed stream ID, so that if
+     RST_STREAM with CANCEL (mandatory?) is sent, we can close all of
+     them. */
 } spdylay_stream;
 
 void spdylay_stream_init(spdylay_stream *stream, int32_t stream_id,
diff --git a/tests/main.c b/tests/main.c
index 76d199f6..dff44e59 100644
--- a/tests/main.c
+++ b/tests/main.c
@@ -73,6 +73,8 @@ int main()
                    test_spdylay_session_add_frame) ||
       !CU_add_test(pSuite, "session_on_syn_stream_received",
                    test_spdylay_session_on_syn_stream_received) ||
+      !CU_add_test(pSuite, "session_on_syn_stream_received_with_push",
+                   test_spdylay_session_on_syn_stream_received_with_push) ||
       !CU_add_test(pSuite, "session_on_syn_reply_received",
                    test_spdylay_session_on_syn_reply_received) ||
       !CU_add_test(pSuite, "session_send_syn_stream",
diff --git a/tests/spdylay_session_test.c b/tests/spdylay_session_test.c
index b6dfc679..e04fe76f 100644
--- a/tests/spdylay_session_test.c
+++ b/tests/spdylay_session_test.c
@@ -279,33 +279,92 @@ void test_spdylay_session_recv_invalid_stream_id()
 void test_spdylay_session_on_syn_stream_received()
 {
   spdylay_session *session;
-  spdylay_session_callbacks callbacks = {
-    NULL,
-    NULL,
-    on_ctrl_recv_callback,
-    on_invalid_ctrl_recv_callback
-  };
+  spdylay_session_callbacks callbacks;
   my_user_data user_data;
   const char *nv[] = { NULL };
   spdylay_frame frame;
   spdylay_stream *stream;
+  int32_t stream_id = 1;
+  uint8_t pri = 3;
+  memset(&callbacks, 0, sizeof(spdylay_session_callbacks));
+  callbacks.on_ctrl_recv_callback = on_ctrl_recv_callback;
+  callbacks.on_invalid_ctrl_recv_callback = on_invalid_ctrl_recv_callback;
+  user_data.valid = 0;
+  user_data.invalid = 0;
+
+  spdylay_session_server_new(&session, &callbacks, &user_data);
+  spdylay_frame_syn_stream_init(&frame.syn_stream, SPDYLAY_FLAG_NONE,
+                                stream_id, 0, pri, dup_nv(nv));
+
+  CU_ASSERT(0 == spdylay_session_on_syn_stream_received(session, &frame));
+  CU_ASSERT(1 == user_data.valid);
+  stream = spdylay_session_get_stream(session, stream_id);
+  CU_ASSERT(SPDYLAY_STREAM_OPENING == stream->state);
+  CU_ASSERT(pri == stream->pri);
+
+  /* Same stream ID twice leads stream closing */
+  CU_ASSERT(0 == spdylay_session_on_syn_stream_received(session, &frame));
+  CU_ASSERT(1 == user_data.invalid);
+  CU_ASSERT(SPDYLAY_STREAM_CLOSING ==
+            spdylay_session_get_stream(session, stream_id)->state);
+
+  /* assoc_stream_id != 0 from client is invalid. */
+  frame.syn_stream.assoc_stream_id = 1;
+  CU_ASSERT(0 == spdylay_session_on_syn_stream_received(session, &frame));
+  CU_ASSERT(2 == user_data.invalid);
+
+  spdylay_frame_syn_stream_free(&frame.syn_stream);
+  spdylay_session_del(session);
+}
+
+void test_spdylay_session_on_syn_stream_received_with_push()
+{
+  spdylay_session *session;
+  spdylay_session_callbacks callbacks;
+  my_user_data user_data;
+  const char *nv[] = { NULL };
+  spdylay_frame frame;
+  spdylay_stream *stream;
+  int32_t stream_id = 2;
+  int32_t assoc_stream_id = 1;
+  uint8_t pri = 3;
+  memset(&callbacks, 0, sizeof(spdylay_session_callbacks));
+  callbacks.on_ctrl_recv_callback = on_ctrl_recv_callback;
+  callbacks.on_invalid_ctrl_recv_callback = on_invalid_ctrl_recv_callback;
   user_data.valid = 0;
   user_data.invalid = 0;
 
   spdylay_session_client_new(&session, &callbacks, &user_data);
-  spdylay_frame_syn_stream_init(&frame.syn_stream, SPDYLAY_FLAG_NONE,
-                                2, 0, 3, dup_nv(nv));
+  spdylay_session_open_stream(session, assoc_stream_id, SPDYLAY_FLAG_NONE,
+                              pri, SPDYLAY_STREAM_OPENED);
+  spdylay_frame_syn_stream_init(&frame.syn_stream,
+                                SPDYLAY_FLAG_UNIDIRECTIONAL,
+                                stream_id, assoc_stream_id, pri, dup_nv(nv));
 
   CU_ASSERT(0 == spdylay_session_on_syn_stream_received(session, &frame));
   CU_ASSERT(1 == user_data.valid);
-  stream = (spdylay_stream*)spdylay_map_find(&session->streams, 2);
+  stream = spdylay_session_get_stream(session, stream_id);
   CU_ASSERT(SPDYLAY_STREAM_OPENING == stream->state);
-  CU_ASSERT(3 == stream->pri);
 
+  /* assoc_stream_id == 0 is invalid */
+  frame.syn_stream.stream_id = 4;
+  frame.syn_stream.assoc_stream_id = 0;
   CU_ASSERT(0 == spdylay_session_on_syn_stream_received(session, &frame));
   CU_ASSERT(1 == user_data.invalid);
-  CU_ASSERT(SPDYLAY_STREAM_CLOSING ==
-            ((spdylay_stream*)spdylay_map_find(&session->streams, 2))->state);
+
+  /* Push without SPDYLAY_FLAG_UNIDIRECTIONAL is invalid */
+  frame.syn_stream.stream_id = 6;
+  frame.syn_stream.assoc_stream_id = 1;
+  frame.syn_stream.hd.flags = SPDYLAY_FLAG_FIN;
+  CU_ASSERT(0 == spdylay_session_on_syn_stream_received(session, &frame));
+  CU_ASSERT(2 == user_data.invalid);
+
+  /* Push to non-existent stream is invalid */
+  frame.syn_stream.stream_id = 8;
+  frame.syn_stream.assoc_stream_id = 3;
+  frame.syn_stream.hd.flags = SPDYLAY_FLAG_UNIDIRECTIONAL;
+  CU_ASSERT(0 == spdylay_session_on_syn_stream_received(session, &frame));
+  CU_ASSERT(3 == user_data.invalid);
 
   spdylay_frame_syn_stream_free(&frame.syn_stream);
   spdylay_session_del(session);
@@ -476,36 +535,6 @@ void test_spdylay_session_reply_fail()
   spdylay_session_del(session);
 }
 
-void test_spdylay_session_on_syn_stream_received_with_unidir_fin()
-{
-  spdylay_session *session;
-  spdylay_session_callbacks callbacks = {
-    NULL,
-    NULL,
-    on_ctrl_recv_callback,
-    NULL
-  };
-  my_user_data user_data;
-  const char *nv[] = { NULL };
-  spdylay_frame frame;
-  spdylay_stream *stream;
-  user_data.valid = 0;
-  user_data.invalid = 0;
-
-  spdylay_session_client_new(&session, &callbacks, &user_data);
-  spdylay_frame_syn_stream_init(&frame.syn_stream,
-                                SPDYLAY_FLAG_FIN | SPDYLAY_FLAG_UNIDIRECTIONAL,
-                                2, 0, 3, dup_nv(nv));
-
-  CU_ASSERT(0 == spdylay_session_on_syn_stream_received(session, &frame));
-  CU_ASSERT(1 == user_data.valid);
-  stream = (spdylay_stream*)spdylay_map_find(&session->streams, 2);
-  CU_ASSERT(NULL == stream);
-
-  spdylay_frame_syn_stream_free(&frame.syn_stream);
-  spdylay_session_del(session);
-}
-
 void test_spdylay_session_on_headers_received()
 {
   spdylay_session *session;
diff --git a/tests/spdylay_session_test.h b/tests/spdylay_session_test.h
index 29a7af4d..6ea99bcd 100644
--- a/tests/spdylay_session_test.h
+++ b/tests/spdylay_session_test.h
@@ -29,6 +29,7 @@ void test_spdylay_session_recv();
 void test_spdylay_session_recv_invalid_stream_id();
 void test_spdylay_session_add_frame();
 void test_spdylay_session_on_syn_stream_received();
+void test_spdylay_session_on_syn_stream_received_with_push();
 void test_spdylay_session_on_syn_reply_received();
 void test_spdylay_session_send_syn_stream();
 void test_spdylay_session_send_syn_reply();