diff --git a/lib/minitest.rb b/lib/minitest.rb
index 14b5680a..136a581d 100644
--- a/lib/minitest.rb
+++ b/lib/minitest.rb
@@ -923,7 +923,7 @@ def backtrace # :nodoc:
 
     def message # :nodoc:
       bt = Minitest.filter_backtrace(self.backtrace)
-      bt = Minitest.filter_backtrace(self.cause.cause.backtrace) + bt if self.cause.cause
+      bt = Minitest.filter_backtrace(self.cause.cause.backtrace) + bt if self.cause && self.cause.cause
       "#{self.error.class}: #{self.error.message}#{bt.map{ |s| "\n    #{s}" }.join}"
     end
 
diff --git a/lib/minitest/mock.rb b/lib/minitest/mock.rb
index 39cfc24e..62594b22 100644
--- a/lib/minitest/mock.rb
+++ b/lib/minitest/mock.rb
@@ -222,9 +222,9 @@ def stub name, val_or_callable, *block_args
 
     metaclass.send :alias_method, new_name, name
 
-    metaclass.send :define_method, name do |*args, &blk|
+    metaclass.send :define_method, name do |*args, **kwargs, &blk|
       if val_or_callable.respond_to? :call then
-        val_or_callable.call(*args, &blk)
+        val_or_callable.call(*args, **kwargs, &blk)
       else
         blk.call(*block_args) if blk
         val_or_callable