diff --git a/panda/src/express/subStreamBuf.cxx b/panda/src/express/subStreamBuf.cxx
index c7ac6381ab..54b52d87af 100644
--- a/panda/src/express/subStreamBuf.cxx
+++ b/panda/src/express/subStreamBuf.cxx
@@ -200,5 +200,5 @@ underflow() {
     _cur += num_bytes;
   }
 
-  return *gptr();
+  return (unsigned char)*gptr();
 }