diff --git a/lib/cmap/message_stream.js b/lib/cmap/message_stream.js
index 8bab9250f74..15a4c75a6a4 100644
--- a/lib/cmap/message_stream.js
+++ b/lib/cmap/message_stream.js
@@ -76,7 +76,8 @@ class MessageStream extends Duplex {
     // TODO: agreed compressor should live in `StreamDescription`
     const shouldCompress = operationDescription && !!operationDescription.agreedCompressor;
     if (!shouldCompress || !canCompress(command)) {
-      this.push(Buffer.concat(command.toBin()));
+      const data = command.toBin();
+      this.push(Array.isArray(data) ? Buffer.concat(data) : data);
       return;
     }