diff --git a/Gemfile b/Gemfile
index 0a3bb9e..1257239 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,4 +1,4 @@
-source :rubygems
+source 'https://rubygems.org'
 
 gemspec :name => "wrong"
 
diff --git a/lib/wrong/adapters/minitest.rb b/lib/wrong/adapters/minitest.rb
index 9fae306..48e30a3 100644
--- a/lib/wrong/adapters/minitest.rb
+++ b/lib/wrong/adapters/minitest.rb
@@ -9,6 +9,11 @@ def failure_class
     MiniTest::Assertion
   end
 
+  if MiniTest::VERSION >= "5.0.6"
+    alias_method :_assertions, :assertions
+    alias_method :"_assertions=", :"assertions="
+  end
+
   def aver(valence, explanation = nil, depth = 0)
     self._assertions += 1 # increment minitest's assert count
     super(valence, explanation, depth + 1) # apparently this passes along the default block