diff --git a/base/loading.jl b/base/loading.jl
index d7d0a4af81382..b030ffa9fde46 100644
--- a/base/loading.jl
+++ b/base/loading.jl
@@ -2022,7 +2022,10 @@ function warn_if_already_loaded_different(uuidkey::PkgId)
                 end
             end
             @warn warnstr
-            push!(already_warned_path_change_pkgs, uuidkey.uuid)
+            # Toplevel modules have a `uuid` of `Nothing`
+            if uuidkey.uuid !== nothing
+                push!(already_warned_path_change_pkgs, uuidkey.uuid)
+            end
         end
     end
 end