diff --git a/lib/cpp/src/transport/TBufferTransports.cpp b/lib/cpp/src/transport/TBufferTransports.cpp
index 9164a1f..0deef1b 100644
--- a/lib/cpp/src/transport/TBufferTransports.cpp
+++ b/lib/cpp/src/transport/TBufferTransports.cpp
@@ -101,7 +101,7 @@
   // The number of bytes of data we have already.
   uint32_t have = rBound_ - rBase_;
   // The number of additional bytes we need from the underlying transport.
-  uint32_t need = *len - have;
+  int32_t need = *len - have;
   // The space from the start of the buffer to the end of our data.
   uint32_t offset = rBound_ - rBuf_.get();
   assert(need > 0);