diff --git a/src/backend/utils/activity/pgstat_io.c b/src/backend/utils/activity/pgstat_io.c
index e03b021af3..0cf5fcf564 100644
--- a/src/backend/utils/activity/pgstat_io.c
+++ b/src/backend/utils/activity/pgstat_io.c
@@ -29,7 +29,8 @@ static bool have_iostats = false;
  * elements.
  */
 #define pgstat_is_ioop_tracked_in_bytes(io_op) \
-	((io_op) < IOOP_NUM_TYPES && (io_op) >= IOOP_EXTEND)
+	(((unsigned int) io_op) < IOOP_NUM_TYPES && \
+	 ((unsigned int) io_op) >= IOOP_EXTEND)
 
 /*
  * Check that stats have not been counted for any combination of IOObject,