diff --git a/lib/minitest.rb b/lib/minitest.rb
index ff7744c1..78c18f14 100644
--- a/lib/minitest.rb
+++ b/lib/minitest.rb
@@ -21,7 +21,10 @@ module Minitest
   # Parallel test executor
 
   mc.send :attr_accessor, :parallel_executor
-  self.parallel_executor = Parallel::Executor.new((ENV["N"] || 2).to_i)
+
+  warn "DEPRECATED: use MT_CPU instead of N for parallel test runs" if ENV["N"]
+  n_threads = (ENV["MT_CPU"] || ENV["N"] || 2).to_i
+  self.parallel_executor = Parallel::Executor.new n_threads
 
   ##
   # Filter object for backtraces.