diff --git a/simgear/misc/zfstream.cxx b/simgear/misc/zfstream.cxx
index 38a16ff2..eae24f78 100644
--- a/simgear/misc/zfstream.cxx
+++ b/simgear/misc/zfstream.cxx
@@ -270,7 +270,7 @@ gzfilebuf::underflow()
     }
     else
     {
-        return fillbuf() == EOF ? traits_type::eof() : int_type(*gptr());
+        return fillbuf() == EOF ? traits_type::eof() : (unsigned char) (*gptr());
     }
 }