diff --git a/lib/ttnt/testtask.rb b/lib/ttnt/testtask.rb
index ee888b9..d8dc538 100644
--- a/lib/ttnt/testtask.rb
+++ b/lib/ttnt/testtask.rb
@@ -71,10 +71,17 @@ def define_run_task
         if tests.empty?
           STDERR.puts 'No test selected.'
         else
-          args =
-            "#{@rake_testtask.ruby_opts_string} #{@rake_testtask.run_code} " +
-            "#{tests.to_a.join(' ')} #{@rake_testtask.option_list}"
-          run_ruby args
+          if ENV['ISOLATED']
+            tests.each do |test|
+              args = "#{@rake_testtask.ruby_opts_string} #{test} #{@rake_testtask.option_list}"
+              run_ruby args
+            end
+          else
+            args =
+              "#{@rake_testtask.ruby_opts_string} #{@rake_testtask.run_code} " +
+              "#{tests.to_a.join(' ')} #{@rake_testtask.option_list}"
+            run_ruby args
+          end
         end
       end
     end
diff --git a/test/integration_test.rb b/test/integration_test.rb
index c322f43..50da4e9 100644
--- a/test/integration_test.rb
+++ b/test/integration_test.rb
@@ -44,6 +44,15 @@ def test_tests_are_selected_based_on_changes_in_current_working_tree
         output = rake('ttnt:test:run')
         assert_match '2 runs, 2 assertions, 2 failures', output[:stdout]
       end
+
+      def test_isolated
+        # Make TTNT select all tests
+        git_rm_and_commit("#{@repo.workdir}/.ttnt", 'Remove .ttnt')
+        ENV['ISOLATED'] = '1'
+        output = rake('ttnt:test:run')
+        ENV.delete('ISOLATED')
+        assert_equal 3, output[:stdout].split('# Running:').count
+      end
     end
 
     class AdditionAmongComments < TTNT::TestCase::AdditionAmongComments