diff --git a/R/compat-downstream-deps.R b/R/compat-downstream-deps.R
index 77bec90d8f..7ee705234a 100644
--- a/R/compat-downstream-deps.R
+++ b/R/compat-downstream-deps.R
@@ -155,7 +155,7 @@ check_downstream <- function(ver,
 
   # Don't ask again. Flip now instead of on exit to defensively
   # prevent recursion.
-  cache[[pkg]][[deps_key]] <- TRUE
+  cache[[pkg]][deps_key] <- list(TRUE)
   env$checked <- TRUE
 
   pkgs <- vapply(deps, `[[`, "", "pkg")