diff --git a/lib/delphi/src/Thrift.Transport.pas b/lib/delphi/src/Thrift.Transport.pas
index 3f22b09..fd08837 100644
--- a/lib/delphi/src/Thrift.Transport.pas
+++ b/lib/delphi/src/Thrift.Transport.pas
@@ -596,7 +596,7 @@
 procedure TEndpointTransportBase.CheckReadBytesAvailable( const numBytes : Int64);
 // Throws if there are not enough bytes in the input stream to satisfy a read of numBytes bytes of data
 begin
-  if RemainingMessageSize < numBytes
+  if (RemainingMessageSize < numBytes) or (numBytes < 0)
   then raise TTransportExceptionEndOfFile.Create('MaxMessageSize reached');
 end;
 
@@ -604,7 +604,7 @@
 procedure TEndpointTransportBase.CountConsumedMessageBytes( const numBytes : Int64);
 // Consumes numBytes from the RemainingMessageSize.
 begin
-  if (RemainingMessageSize >= numBytes)
+  if (RemainingMessageSize >= numBytes) and (numBytes >= 0)
   then Dec( FRemainingMessageSize, numBytes)
   else begin
     FRemainingMessageSize := 0;