diff --git a/tests/acceptance/flexnbd/fake_source.rb b/tests/acceptance/flexnbd/fake_source.rb
index 888ac33..793b647 100644
--- a/tests/acceptance/flexnbd/fake_source.rb
+++ b/tests/acceptance/flexnbd/fake_source.rb
@@ -53,6 +53,10 @@ module FlexNBD
     def write_write_request(from, len, handle = 'myhandle')
       send_request(1, handle, from, len)
     end
+    
+    def write_flush_request(handle = 'myhandle')
+      send_request(3, handle, 0, 0)
+    end
 
     def write_entrust_request(handle = 'myhandle')
       send_request(65_536, handle)
@@ -95,6 +99,10 @@ module FlexNBD
       write_data(data)
     end
 
+    def flush
+      write_flush_request
+    end
+
     def read_response
       magic = @sock.read(4)
       error_s = @sock.read(4)
diff --git a/tests/acceptance/test_serve_mode.rb b/tests/acceptance/test_serve_mode.rb
index 1d12dd9..faa0ce0 100644
--- a/tests/acceptance/test_serve_mode.rb
+++ b/tests/acceptance/test_serve_mode.rb
@@ -24,7 +24,9 @@ class TestServeMode < Test::Unit::TestCase
       assert_equal 'NBDMAGIC', result[:passwd]
       assert_equal 0x00420281861253, result[:magic]
       assert_equal @env.file1.size, result[:size]
-      assert_equal 13, result[:flags]
+      # See src/common/nbdtypes.h for the various flags. At the moment we
+      # support HAS_FLAGS (1), SEND_FLUSH (4), SEND_FUA (8)
+      assert_equal (1 | 4 | 8), result[:flags]
       assert_equal "\x0" * 124, result[:reserved]
       yield client
     ensure
@@ -106,4 +108,14 @@ class TestServeMode < Test::Unit::TestCase
       assert_equal FlexNBD::REPLY_MAGIC, rsp[:magic]
     end
   end
+
+  def test_flush_is_accepted
+    connect_to_server do |client|
+      # Start with a file of all-zeroes.
+      client.flush
+      rsp = client.read_response
+      assert_equal FlexNBD::REPLY_MAGIC, rsp[:magic]
+      assert_equal 0, rsp[:error]
+    end
+  end
 end