diff --git a/src/compression.jl b/src/compression.jl
index ee518ea..8a7f841 100644
--- a/src/compression.jl
+++ b/src/compression.jl
@@ -180,15 +180,30 @@ function TranscodingStreams.startproc(codec::ZstdCompressor, mode::Symbol, err::
         end
         # TODO Allow setting other parameters here.
     end
-    code = reset!(codec.cstream, 0 #=unknown source size=#)
-    if iserror(code)
-        # This is unreachable according to zstd.h
-        err[] = ErrorException("zstd error resetting context.")
-        return :error
-    end
+    reset!(codec.cstream)
     return :ok
 end
 
+@static if isdefined(TranscodingStreams, :pledgeinsize) # Defined in v0.11.3
+    function TranscodingStreams.pledgeinsize(codec::ZstdCompressor, insize::Int64, err::Error)::Symbol
+        if codec.cstream.ptr == C_NULL
+            error("`startproc` must be called before `pledgeinsize`")
+        end
+        srcsize = if signbit(insize)
+            ZSTD_CONTENTSIZE_UNKNOWN
+        else
+            Culonglong(insize)
+        end
+        code = LibZstd.ZSTD_CCtx_setPledgedSrcSize(codec.cstream, srcsize)
+        if iserror(code)
+            err[] = ErrorException("zstd error setting pledged source size")
+            :error
+        else
+            :ok
+        end
+    end
+end
+
 function TranscodingStreams.process(codec::ZstdCompressor, input::Memory, output::Memory, err::Error)
     if codec.cstream.ptr == C_NULL
         error("startproc must be called before process")
diff --git a/src/libzstd.jl b/src/libzstd.jl
index c62bf0c..ca980bf 100644
--- a/src/libzstd.jl
+++ b/src/libzstd.jl
@@ -60,23 +60,17 @@ Base.unsafe_convert(::Type{Ptr{LibZstd.ZSTD_CCtx}}, cstream::CStream) = cstream.
 Base.unsafe_convert(::Type{Ptr{InBuffer}}, cstream::CStream) = Base.unsafe_convert(Ptr{InBuffer}, cstream.ibuffer)
 Base.unsafe_convert(::Type{Ptr{OutBuffer}}, cstream::CStream) = Base.unsafe_convert(Ptr{OutBuffer}, cstream.obuffer)
 
-function reset!(cstream::CStream, srcsize::Integer)
+function reset!(cstream::CStream)
     # ZSTD_resetCStream is deprecated
     # https://github.com/facebook/zstd/blob/9d2a45a705e22ad4817b41442949cd0f78597154/lib/zstd.h#L2253-L2272
     res = LibZstd.ZSTD_CCtx_reset(cstream, LibZstd.ZSTD_reset_session_only)
-    if iserror(res)
-        return res
-    end
-    if srcsize == 0
-        # From zstd.h:
-        # Note: ZSTD_resetCStream() interprets pledgedSrcSize == 0 as ZSTD_CONTENTSIZE_UNKNOWN, but
-        # ZSTD_CCtx_setPledgedSrcSize() does not do the same, so ZSTD_CONTENTSIZE_UNKNOWN must be
-        # explicitly specified.
-        srcsize = ZSTD_CONTENTSIZE_UNKNOWN
-    end
     reset!(cstream.ibuffer)
     reset!(cstream.obuffer)
-    return LibZstd.ZSTD_CCtx_setPledgedSrcSize(cstream, srcsize)
+    if iserror(res)
+        # According to zstd.h "Resetting session never fails" so this branch should be unreachable.
+        error("unreachable")
+    end
+    return
 end
 
 """
diff --git a/test/runtests.jl b/test/runtests.jl
index e403bf2..5d510c6 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -130,9 +130,17 @@ include("utils.jl")
         @test CodecZstd.find_decompressed_size(v) == 22
 
         codec = ZstdCompressor
-        buffer3 = transcode(codec, b"Hello")
-        buffer4 = transcode(codec, b"World!")
+        sink = IOBuffer()
+        s = TranscodingStream(codec(), sink; stop_on_end=true)
+        write(s, b"Hello")
+        close(s)
+        buffer3 = take!(sink)
         @test CodecZstd.find_decompressed_size(buffer3) == CodecZstd.ZSTD_CONTENTSIZE_UNKNOWN
+        sink = IOBuffer()
+        s = TranscodingStream(codec(), sink; stop_on_end=true)
+        write(s, b"Hello")
+        close(s)
+        buffer4 = take!(sink)
         @test CodecZstd.find_decompressed_size(buffer4) == CodecZstd.ZSTD_CONTENTSIZE_UNKNOWN
 
         write(iob, buffer1)
@@ -156,6 +164,68 @@ include("utils.jl")
         @test CodecZstd.find_decompressed_size(v) == CodecZstd.ZSTD_CONTENTSIZE_ERROR
     end
 
+    if isdefined(TranscodingStreams, :pledgeinsize)
+        @testset "pledgeinsize" begin
+            # when pledgeinsize is available transcode should save the 
+            # decompressed size in a header
+            for n in [0:30; 1000; 1000000;]
+                v = transcode(ZstdCompressor, rand(UInt8, n))
+                @test CodecZstd.find_decompressed_size(v) == n
+            end
+
+            # Test what happens if pledgeinsize promise is broken
+            d1 = zeros(UInt8, 10000)
+            d2 = zeros(UInt8, 10000)
+            GC.@preserve d1 d2 begin
+                @testset "too many bytes" begin
+                    m1 = TranscodingStreams.Memory(pointer(d1), 1000)
+                    m2 = TranscodingStreams.Memory(pointer(d2), 1000)
+                    codec = ZstdCompressor()
+                    e = TranscodingStreams.Error()
+                    @test TranscodingStreams.startproc(codec, :read, e) === :ok
+                    @test TranscodingStreams.pledgeinsize(codec, Int64(10), e) === :ok
+                    @test TranscodingStreams.process(codec, m1, m2, e) === (0, 0, :error)
+                    @test e[] == ErrorException("zstd compression error: Src size is incorrect")
+                    TranscodingStreams.finalize(codec)
+                end
+                @testset "too few bytes" begin
+                    m1 = TranscodingStreams.Memory(pointer(d1), 10)
+                    m2 = TranscodingStreams.Memory(pointer(d2), 1000)
+                    codec = ZstdCompressor()
+                    e = TranscodingStreams.Error()
+                    @test TranscodingStreams.startproc(codec, :read, e) === :ok
+                    @test TranscodingStreams.pledgeinsize(codec, Int64(10000), e) === :ok
+                    @test TranscodingStreams.process(codec, m1, m2, e)[3] === :ok
+                    m1 = TranscodingStreams.Memory(pointer(d1), 0)
+                    @test TranscodingStreams.process(codec, m1, m2, e)[3] === :error
+                    @test e[] == ErrorException("zstd compression error: Src size is incorrect")
+                    TranscodingStreams.finalize(codec)
+                end
+                @testset "set pledgeinsize after process" begin
+                    m1 = TranscodingStreams.Memory(pointer(d1), 1000)
+                    m2 = TranscodingStreams.Memory(pointer(d2), 1000)
+                    codec = ZstdCompressor()
+                    e = TranscodingStreams.Error()
+                    @test TranscodingStreams.startproc(codec, :read, e) === :ok
+                    @test TranscodingStreams.process(codec, m1, m2, e)[3] === :ok
+                    @test TranscodingStreams.pledgeinsize(codec, Int64(10000), e) === :error
+                    @test e[] == ErrorException("zstd error setting pledged source size")
+                    TranscodingStreams.finalize(codec)
+                end
+                @testset "set unknown pledgeinsize" begin
+                    m1 = TranscodingStreams.Memory(pointer(d1), 1000)
+                    m2 = TranscodingStreams.Memory(pointer(d2), 1000)
+                    codec = ZstdCompressor()
+                    e = TranscodingStreams.Error()
+                    @test TranscodingStreams.startproc(codec, :read, e) === :ok
+                    @test TranscodingStreams.pledgeinsize(codec, Int64(-1), e) === :ok
+                    @test TranscodingStreams.process(codec, m1, m2, e)[3] === :ok
+                    TranscodingStreams.finalize(codec)
+                end
+            end
+        end
+    end
+
     include("compress_endOp.jl")
     include("static_only_tests.jl")
 
@@ -195,6 +265,10 @@ include("utils.jl")
             TranscodingStreams.finalize(codec)
             data = [0x00,0x01]
             GC.@preserve data let m = TranscodingStreams.Memory(pointer(data), length(data))
+                try
+                    TranscodingStreams.pledgeinsize(codec, Int64(10), TranscodingStreams.Error())
+                catch
+                end
                 try
                     TranscodingStreams.expectedsize(codec, m)
                 catch