diff --git a/include/grpc/byte_buffer_reader.h b/include/grpc/byte_buffer_reader.h
index 6386db6..a9cbb77 100644
--- a/include/grpc/byte_buffer_reader.h
+++ b/include/grpc/byte_buffer_reader.h
@@ -42,7 +42,7 @@
   /* Different current objects correspond to different types of byte buffers */
   union {
     /* Index into a slice buffer's array of slices */
-    int index;
+    unsigned index;
   } current;
 };