diff --git a/src/client.rs b/src/client.rs
index bea78b3..8574e3c 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -57,7 +57,7 @@ impl Peer for Client {
     }
 
     fn is_valid_remote_stream_id(id: StreamId) -> bool {
-        id.is_server_initiated()
+        false
     }
 
     fn convert_send_message(
diff --git a/src/error.rs b/src/error.rs
index 606c3d9..4b82bb4 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -56,6 +56,9 @@ pub enum User {
     /// The stream is not currently expecting a frame of this type.
     UnexpectedFrameType,
 
+    /// The connection state is corrupt and the connection should be dropped.
+    Corrupt,
+
     // TODO: reserve additional variants
 }
 
@@ -93,6 +96,7 @@ macro_rules! user_desc {
             InvalidStreamId => concat!($prefix, "invalid stream ID"),
             InactiveStreamId => concat!($prefix, "inactive stream ID"),
             UnexpectedFrameType => concat!($prefix, "unexpected frame type"),
+            Corrupt => concat!($prefix, "connection state corrupt"),
         }
     });
 }
diff --git a/src/proto/connection.rs b/src/proto/connection.rs
index f480ebf..ca93c49 100644
--- a/src/proto/connection.rs
+++ b/src/proto/connection.rs
@@ -23,6 +23,8 @@ use std::hash::BuildHasherDefault;
 pub struct Connection<T, P, B: IntoBuf = Bytes> {
     inner: proto::Inner<T, B::Buf>,
     streams: StreamMap<State>,
+    // Set to `true` as long as the connection is in a valid state.
+    active: bool,
     peer: PhantomData<(P, B)>,
 }
 
@@ -36,6 +38,7 @@ pub fn new<T, P, B>(transport: proto::Inner<T, B::Buf>) -> Connection<T, P, B>
     Connection {
         inner: transport,
         streams: StreamMap::default(),
+        active: true,
         peer: PhantomData,
     }
 }
@@ -108,6 +111,10 @@ impl<T, P, B> Stream for Connection<T, P, B>
 
         trace!("Connection::poll");
 
+        if !self.active {
+            return Err(error::User::Corrupt.into());
+        }
+
         let frame = match try!(self.inner.poll()) {
             Async::Ready(f) => f,
             Async::NotReady => {
@@ -135,7 +142,8 @@ impl<T, P, B> Stream for Connection<T, P, B>
                     // connections should not be factored.
 
                     if !P::is_valid_remote_stream_id(stream_id) {
-                        unimplemented!();
+                        self.active = false;
+                        return Err(error::Reason::ProtocolError.into());
                     }
                 }
 
@@ -179,6 +187,10 @@ impl<T, P, B> Sink for Connection<T, P, B>
     fn start_send(&mut self, item: Self::SinkItem)
         -> StartSend<Self::SinkItem, Self::SinkError>
     {
+        if !self.active {
+            return Err(error::User::Corrupt.into());
+        }
+
         // First ensure that the upstream can process a new item
         if !try!(self.poll_ready()).is_ready() {
             return Ok(AsyncSink::NotReady(item));
diff --git a/src/server.rs b/src/server.rs
index fe40040..ff8411d 100644
--- a/src/server.rs
+++ b/src/server.rs
@@ -111,7 +111,7 @@ impl Peer for Server {
     type Poll = http::request::Head;
 
     fn is_valid_local_stream_id(id: StreamId) -> bool {
-        id.is_server_initiated()
+        false
     }
 
     fn is_valid_remote_stream_id(id: StreamId) -> bool {
diff --git a/tests/client_request.rs b/tests/client_request.rs
index 47f198a..6baea71 100644
--- a/tests/client_request.rs
+++ b/tests/client_request.rs
@@ -23,6 +23,17 @@ macro_rules! assert_user_err {
     }};
 }
 
+macro_rules! assert_proto_err {
+    ($actual:expr, $err:ident) => {{
+        use h2::error::{ConnectionError, Reason};
+
+        match $actual {
+            ConnectionError::Proto(e) => assert_eq!(e, Reason::$err),
+            _ => panic!("unexpected connection error type"),
+        }
+    }};
+}
+
 #[test]
 fn handshake() {
     let _ = ::env_logger::init();
@@ -341,8 +352,32 @@ fn invalid_client_stream_id() {
 }
 
 #[test]
-#[ignore]
 fn invalid_server_stream_id() {
+    let _ = ::env_logger::init();
+
+    let mock = mock_io::Builder::new()
+        .handshake()
+        // Write GET /
+        .write(&[
+               0, 0, 0x10, 1, 5, 0, 0, 0, 1, 0x82, 0x87, 0x41, 0x8B, 0x9D, 0x29,
+                0xAC, 0x4B, 0x8F, 0xA8, 0xE9, 0x19, 0x97, 0x21, 0xE9, 0x84,
+        ])
+        .write(SETTINGS_ACK)
+        // Read response
+        .read(&[0, 0, 1, 1, 5, 0, 0, 0, 2, 137])
+        .build();
+
+    let h2 = client::handshake(mock)
+        .wait().unwrap();
+
+    // Send the request
+    let mut request = request::Head::default();
+    request.uri = "https://http2.akamai.com/".parse().unwrap();
+    let h2 = h2.send_request(1.into(), request, true).wait().unwrap();
+
+    // Get the response
+    let (err, _) = h2.into_future().wait().unwrap_err();
+    assert_proto_err!(err, ProtocolError);
 }
 
 #[test]