diff --git a/common/rdr/FileInStream.cxx b/common/rdr/FileInStream.cxx
index 6d23aa2..8d5c22e 100644
--- a/common/rdr/FileInStream.cxx
+++ b/common/rdr/FileInStream.cxx
@@ -58,7 +58,7 @@
 
 int FileInStream::overrun(int itemSize, int nItems, bool wait)
 {
-  if (itemSize > sizeof(b))
+  if (itemSize > (int)sizeof(b))
     throw Exception("FileInStream overrun: max itemSize exceeded");
 
   if (end - ptr != 0)