diff --git a/R/gh-repo.R b/R/gh-repo.R
index a725df1e..31d7c632 100644
--- a/R/gh-repo.R
+++ b/R/gh-repo.R
@@ -252,7 +252,8 @@ ghrepo <- local({
       ""
     )
 
-    inst$build_time <- inst$build_time %||% NA_real_
+    inst$build_time <- inst$build_time %||%
+      as.difftime(NA_real_, units = "secs")
     cols <- data_frame(
       package = inst$package,
       "old" = oldver,