diff --git a/src/errors.rs b/src/errors.rs
index 0ab6784..c997fd3 100644
--- a/src/errors.rs
+++ b/src/errors.rs
@@ -26,6 +26,8 @@ pub enum DeserializationError {
     InvalidClientCommand(u8),
     #[error("Invalid server status {0}; expected 0-8")]
     InvalidServerResponse(u8),
+    #[error("Invalid byte in reserved byte ({0})")]
+    InvalidReservedByte(u8),
 }
 
 #[test]
@@ -86,6 +88,10 @@ impl PartialEq for DeserializationError {
                 &DeserializationError::InvalidServerResponse(a),
                 &DeserializationError::InvalidServerResponse(b),
             ) => a == b,
+            (
+                &DeserializationError::InvalidReservedByte(a),
+                &DeserializationError::InvalidReservedByte(b),
+            ) => a == b,
             (_, _) => false,
         }
     }
diff --git a/src/messages/client_command.rs b/src/messages/client_command.rs
index a8beabc..44ac669 100644
--- a/src/messages/client_command.rs
+++ b/src/messages/client_command.rs
@@ -32,9 +32,9 @@ impl ClientConnectionRequest {
     pub async fn read<R: AsyncRead + Send + Unpin>(
         r: &mut R,
     ) -> Result<Self, DeserializationError> {
-        let mut buffer = [0; 2];
+        let mut buffer = [0; 3];
 
-        read_amt(r, 2, &mut buffer).await?;
+        read_amt(r, 3, &mut buffer).await?;
 
         if buffer[0] != 5 {
             return Err(DeserializationError::InvalidVersion(5, buffer[0]));
@@ -47,6 +47,10 @@ impl ClientConnectionRequest {
             x => return Err(DeserializationError::InvalidClientCommand(x)),
         };
 
+        if buffer[2] != 0 {
+            return Err(DeserializationError::InvalidReservedByte(buffer[2]));
+        }
+
         let destination_address = SOCKSv5Address::read(r).await?;
 
         read_amt(r, 2, &mut buffer).await?;
@@ -69,7 +73,7 @@ impl ClientConnectionRequest {
             ClientConnectionCommand::AssociateUDPPort => 3,
         };
 
-        w.write_all(&[5, command]).await?;
+        w.write_all(&[5, command, 0]).await?;
         self.destination_address.write(w).await?;
         w.write_all(&[
             (self.destination_port >> 8) as u8,