diff --git a/lib/cpp/src/thrift/transport/TBufferTransports.cpp b/lib/cpp/src/thrift/transport/TBufferTransports.cpp
index 4bb8713..534067f 100644
--- a/lib/cpp/src/thrift/transport/TBufferTransports.cpp
+++ b/lib/cpp/src/thrift/transport/TBufferTransports.cpp
@@ -372,7 +372,7 @@
   }
 
   // Allocate into a new pointer so we don't bork ours if it fails.
-  auto* new_buffer = static_cast<uint8_t*>(std::realloc(buffer_, new_size));
+  auto* new_buffer = static_cast<uint8_t*>(std::realloc(buffer_, static_cast<std::size_t>(new_size)));
   if (new_buffer == nullptr) {
     throw std::bad_alloc();
   }