diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 18a8d850..f5cdfcdf 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -26,6 +26,13 @@ jobs:
           - windows-latest
         arch:
           - x64
+        include:
+          - os: ubuntu-latest
+            version: '1'
+            arch: x86
+          - os: macOS-14
+            version: '1'
+            arch: aarch64
     steps:
       - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@v1
diff --git a/ext/TestExt.jl b/ext/TestExt.jl
index b7c7de36..a1a15668 100644
--- a/ext/TestExt.jl
+++ b/ext/TestExt.jl
@@ -89,6 +89,7 @@ function TranscodingStreams.test_chunked_read(Encoder, Decoder)
         for chunk in chunks
             stream = TranscodingStream(Decoder(), buffer, stop_on_end=true)
             ok &= read(stream) == chunk
+            ok &= position(stream) == length(chunk)
             ok &= eof(stream)
             ok &= isreadable(stream)
             close(stream)
diff --git a/fuzz/fuzz.jl b/fuzz/fuzz.jl
index 10b48060..ef36dcc5 100644
--- a/fuzz/fuzz.jl
+++ b/fuzz/fuzz.jl
@@ -120,8 +120,7 @@ end
     for r in rs
         d = r(stream)
         append!(x, d)
-        # TODO fix position
-        # length(x) == position(stream) || return false
+        length(x) == position(stream) || return false
     end
     x == data[eachindex(x)]
 end
diff --git a/src/noop.jl b/src/noop.jl
index 9ece4e1f..e555ba07 100644
--- a/src/noop.jl
+++ b/src/noop.jl
@@ -53,16 +53,18 @@ Note that this method may return a wrong position when
 - some data have been inserted by `TranscodingStreams.unread`, or
 - the position of the wrapped stream has been changed outside of this package.
 """
-function Base.position(stream::NoopStream)
+function Base.position(stream::NoopStream)::Int64
     mode = stream.state.mode
-    if mode === :idle
+    if !isopen(stream)
+        throw_invalid_mode(mode)
+    elseif mode === :idle
         return Int64(0)
+    elseif has_sharedbuf(stream)
+        return position(stream.stream)
     elseif mode === :write
         return position(stream.stream) + buffersize(stream.buffer1)
-    elseif mode === :read
+    else # read
         return position(stream.stream) - buffersize(stream.buffer1)
-    else
-        throw_invalid_mode(mode)
     end
     @assert false "unreachable"
 end
@@ -97,8 +99,25 @@ function Base.seekend(stream::NoopStream)
     return stream
 end
 
-function Base.unsafe_write(stream::NoopStream, input::Ptr{UInt8}, nbytes::UInt)
+function Base.write(stream::NoopStream, b::UInt8)::Int
+    changemode!(stream, :write)
+    if has_sharedbuf(stream)
+        # directly write data to the underlying stream
+        n = Int(write(stream.stream, b))
+        return n
+    end
+    buffer1 = stream.buffer1
+    marginsize(buffer1) > 0 || flushbuffer(stream)
+    return writebyte!(buffer1, b)
+end
+
+function Base.unsafe_write(stream::NoopStream, input::Ptr{UInt8}, nbytes::UInt)::Int
     changemode!(stream, :write)
+    if has_sharedbuf(stream)
+        # directly write data to the underlying stream
+        n = Int(unsafe_write(stream.stream, input, nbytes))
+        return n
+    end
     buffer = stream.buffer1
     if marginsize(buffer) ≥ nbytes
         copydata!(buffer, input, nbytes)
@@ -106,7 +125,8 @@ function Base.unsafe_write(stream::NoopStream, input::Ptr{UInt8}, nbytes::UInt)
     else
         flushbuffer(stream)
         # directly write data to the underlying stream
-        return unsafe_write(stream.stream, input, nbytes)
+        n = Int(unsafe_write(stream.stream, input, nbytes))
+        return n
     end
 end
 
@@ -152,7 +172,7 @@ function fillbuffer(stream::NoopStream; eager::Bool = false)::Int
     changemode!(stream, :read)
     buffer = stream.buffer1
     @assert buffer === stream.buffer2
-    if stream.stream isa TranscodingStream && buffer === stream.stream.buffer1
+    if has_sharedbuf(stream)
         # Delegate the operation when buffers are shared.
         underlying_mode::Symbol = stream.stream.state.mode
         if underlying_mode === :idle || underlying_mode === :read
diff --git a/src/stream.jl b/src/stream.jl
index 0eae4982..347f7407 100644
--- a/src/stream.jl
+++ b/src/stream.jl
@@ -157,6 +157,10 @@ end
 # throw ArgumentError that mode is invalid.
 throw_invalid_mode(mode) = throw(ArgumentError(string("invalid mode :", mode)))
 
+# Return true if the stream shares buffers with underlying stream
+function has_sharedbuf(stream::TranscodingStream)::Bool
+    stream.stream isa TranscodingStream && stream.buffer2 === stream.stream.buffer1
+end
 
 # Base IO Functions
 # -----------------
@@ -264,7 +268,7 @@ function Base.position(stream::TranscodingStream)
     mode = stream.state.mode
     if mode === :idle
         return Int64(0)
-    elseif mode === :read
+    elseif mode === :read || mode === :stop
         return stats(stream).out
     elseif mode === :write
         return stats(stream).in
@@ -584,7 +588,7 @@ function stats(stream::TranscodingStream)
     buffer2 = stream.buffer2
     if mode === :idle
         transcoded_in = transcoded_out = in = out = 0
-    elseif mode === :read
+    elseif mode === :read || mode === :stop
         transcoded_in = buffer2.transcoded
         transcoded_out = buffer1.transcoded
         in = transcoded_in + buffersize(buffer2)
diff --git a/test/codecdoubleframe.jl b/test/codecdoubleframe.jl
index f3b5076d..1ebeee02 100644
--- a/test/codecdoubleframe.jl
+++ b/test/codecdoubleframe.jl
@@ -272,6 +272,7 @@ DoubleFrameDecoderStream(stream::IO; kwargs...) = TranscodingStream(DoubleFrameD
             )
         ))
         @test read(s1) == b""
+        @test position(s1) == 0
         @test eof(s1)
 
         s2 = NoopStream(
@@ -281,6 +282,7 @@ DoubleFrameDecoderStream(stream::IO; kwargs...) = TranscodingStream(DoubleFrameD
             )
         )
         @test read(s2) == b""
+        @test position(s1) == 0
         @test eof(s2)
     end
 
diff --git a/test/codecnoop.jl b/test/codecnoop.jl
index 3583cbdc..8b988749 100644
--- a/test/codecnoop.jl
+++ b/test/codecnoop.jl
@@ -50,11 +50,11 @@
     close(stream)
 
     stream = TranscodingStream(Noop(), IOBuffer(b"foobarbaz"))
-    @test position(stream) === 0
+    @test position(stream) === Int64(0)
     read(stream, UInt8)
-    @test position(stream) === 1
+    @test position(stream) === Int64(1)
     read(stream)
-    @test position(stream) === 9
+    @test position(stream) === Int64(9)
 
     data = collect(0x00:0x0f)
     stream = TranscodingStream(Noop(), IOBuffer(data))
@@ -368,6 +368,41 @@
                 @test position(stream) == pos
             end
         end
+
+        @testset "writing nested NoopStream sharedbuf=$(sharedbuf)" for sharedbuf in (true, false)
+            stream = NoopStream(NoopStream(IOBuffer()); sharedbuf, bufsize=4)
+            @test position(stream) == 0
+            write(stream, 0x01)
+            @test position(stream) == 1
+            flush(stream)
+            @test position(stream) == 1
+            write(stream, "abc")
+            @test position(stream) == 4
+            flush(stream)
+            @test position(stream) == 4
+            for i in 1:10
+                write(stream, 0x01)
+                @test position(stream) == 4 + i
+            end
+        end
+
+        @testset "reading nested NoopStream sharedbuf=$(sharedbuf)" for sharedbuf in (true, false)
+            stream = NoopStream(NoopStream(IOBuffer("abcdefghijk")); sharedbuf, bufsize=4)
+            @test position(stream) == 0
+            @test !eof(stream)
+            @test position(stream) == 0
+            @test read(stream, UInt8) == b"a"[1]
+            @test position(stream) == 1
+            @test read(stream, 3) == b"bcd"
+            @test position(stream) == 4
+            @test !eof(stream)
+            @test position(stream) == 4
+            @test read(stream) == b"efghijk"
+            @test position(stream) == 11
+            @test eof(stream)
+            @test position(stream) == 11
+        end
+
     end
 
     @testset "seek doesn't delete data" begin
diff --git a/test/codecquadruple.jl b/test/codecquadruple.jl
index 1e17db94..31a0ef53 100644
--- a/test/codecquadruple.jl
+++ b/test/codecquadruple.jl
@@ -51,19 +51,19 @@ end
     close(stream)
 
     stream = TranscodingStream(QuadrupleCodec(), IOBuffer("foo"))
-    @test position(stream) === 0
+    @test position(stream) === Int64(0)
     read(stream, 3)
-    @test position(stream) === 3
+    @test position(stream) === Int64(3)
     read(stream, UInt8)
-    @test position(stream) === 4
+    @test position(stream) === Int64(4)
     close(stream)
 
     stream = TranscodingStream(QuadrupleCodec(), IOBuffer())
-    @test position(stream) === 0
+    @test position(stream) === Int64(0)
     write(stream, 0x00)
-    @test position(stream) === 1
+    @test position(stream) === Int64(1)
     write(stream, "foo")
-    @test position(stream) === 4
+    @test position(stream) === Int64(4)
     close(stream)
 
     # Buffers are shared.