diff --git a/lib/sidekiq/cli.rb b/lib/sidekiq/cli.rb
index c8c050c2..84cb2a3d 100644
--- a/lib/sidekiq/cli.rb
+++ b/lib/sidekiq/cli.rb
@@ -182,7 +182,11 @@ module Sidekiq
     end
 
     def set_environment(cli_env)
-      @environment = cli_env || ENV["RAILS_ENV"] || ENV["RACK_ENV"] || "development"
+      # See #984 for discussion.
+      # APP_ENV is now the preferred ENV term since it is not tech-specific.
+      # Both Sinatra 2.0+ and Sidekiq support this term.
+      # RACK_ENV and RAILS_ENV are there for legacy support.
+      @environment = cli_env || ENV["APP_ENV"] || ENV["RACK_ENV"] || ENV["RAILS_ENV"] || "development"
     end
 
     def symbolize_keys_deep!(hash)