Protocol error with HTTP/2 and Expect: 100-continue persists

$ curl --http2 -X PUT  localhost:8080/ -d foo -X PUT -H 'Expect: 100-continue' --http2-prior-knowledge -v
*   Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to localhost (127.0.0.1) port 8080 (#0)
* Using HTTP2, server supports multi-use
* Connection state changed (HTTP/2 confirmed)
* Copying HTTP/2 data in stream buffer to connection buffer after upgrade: len=0
* Using Stream ID: 1 (easy handle 0x55a9becbe6b0)
> PUT / HTTP/2
> Host: localhost:8080
> User-Agent: curl/7.61.1
> Accept: */*
> Expect: 100-continue
> Content-Length: 3
> Content-Type: application/x-www-form-urlencoded
> 
* Connection state changed (MAX_CONCURRENT_STREAMS == 4294967295)!
* HTTP/2 stream 0 was not closed cleanly: PROTOCOL_ERROR (err 1)
* stopped the pause stream!
* Connection #0 to host localhost left intact
curl: (92) HTTP/2 stream 0 was not closed cleanly: PROTOCOL_ERROR (err 1)

http2 error: Invalid HTTP header field was received: frame type: 1, stream: 1, name: [content-length], value: [0]