diff --git a/lib/minitest.rb b/lib/minitest.rb
index ae0f2ab2..c951d909 100644
--- a/lib/minitest.rb
+++ b/lib/minitest.rb
@@ -139,7 +139,10 @@ def self.run args = []
 
     options = process_args args
 
-    Minitest.const_set :SEED, options[:seed] unless defined?(Minitest::SEED)
+    unless defined?(Minitest::SEED) && Minitest::SEED then
+      remove_const :SEED
+      const_set :SEED, options[:seed]
+    end
 
     reporter = CompositeReporter.new
     reporter << SummaryReporter.new(options[:io], options)
diff --git a/test/minitest/test_minitest_test.rb b/test/minitest/test_minitest_test.rb
index 644bc5a8..b1519841 100644
--- a/test/minitest/test_minitest_test.rb
+++ b/test/minitest/test_minitest_test.rb
@@ -334,6 +334,10 @@ def test_failure
     end
   end
 
+  def test_seed # this is set for THIS run, so I'm not testing it's actual value
+    assert_instance_of Integer, Minitest::SEED
+  end
+
   def test_run_failing_filtered
     setup_basic_tu