diff --git a/lib/cpp/src/transport/TZlibTransport.cpp b/lib/cpp/src/transport/TZlibTransport.cpp
index ea0b0a4..27aa350 100644
--- a/lib/cpp/src/transport/TZlibTransport.cpp
+++ b/lib/cpp/src/transport/TZlibTransport.cpp
@@ -238,7 +238,7 @@
   // Don't try to be clever with shifting buffers.
   // If we have enough data, give a pointer to it,
   // otherwise let the protcol use its slow path.
-  if (readAvail() >= (int)len) {
+  if (readAvail() >= (int)*len) {
     *len = (uint32_t)readAvail();
     return urbuf_ + urpos_;
   }