diff --git a/src/stream.jl b/src/stream.jl
index 0fca6026..2300e6bc 100644
--- a/src/stream.jl
+++ b/src/stream.jl
@@ -282,9 +282,10 @@ end
 # ---------------
 
 function Base.seekstart(stream::TranscodingStream)
+    checkmode(stream)
     mode = stream.state.mode
-    @checkmode (:idle, :read, :write)
-    if mode == :read || mode == :write
+    @checkmode (:idle, :read)
+    if mode == :read
         callstartproc(stream, mode)
         emptybuffer!(stream.state.buffer1)
         emptybuffer!(stream.state.buffer2)
diff --git a/test/codecquadruple.jl b/test/codecquadruple.jl
index 18a40753..b3d710e4 100644
--- a/test/codecquadruple.jl
+++ b/test/codecquadruple.jl
@@ -113,14 +113,10 @@ end
         stream = TranscodingStream(QuadrupleCodec(), sink, bufsize=16)
         write(stream, "x")
         # seekstart must not delete user data even if it errors.
-        try
-            seekstart(stream)
-        catch e
-            e isa ArgumentError || rethrow()
-        end
+        @test_throws ArgumentError seekstart(stream)
         write(stream, TranscodingStreams.TOKEN_END)
         flush(stream)
-        @test_broken take!(sink) == b"xxxx"
+        @test take!(sink) == b"xxxx"
         close(stream)
     end
 end