diff --git a/Library/Homebrew/dev-cmd/test.rb b/Library/Homebrew/dev-cmd/test.rb
index a8661179fb..c678171acb 100644
--- a/Library/Homebrew/dev-cmd/test.rb
+++ b/Library/Homebrew/dev-cmd/test.rb
@@ -83,7 +83,7 @@ module Homebrew
             exec(*args)
           end
         end
-      rescue MiniTest::Assertion => e
+      rescue ::Test::Unit::AssertionFailedError => e
         ofail "#{f.full_name}: failed"
         puts e.message
       rescue Exception => e
diff --git a/Library/Homebrew/formula_assertions.rb b/Library/Homebrew/formula_assertions.rb
index f81087a3dd..2ba5767a71 100644
--- a/Library/Homebrew/formula_assertions.rb
+++ b/Library/Homebrew/formula_assertions.rb
@@ -3,6 +3,11 @@ module Homebrew
     require "test/unit/assertions"
     include ::Test::Unit::Assertions
 
+    # TODO: remove this when we no longer support Ruby 2.0.
+    unless defined?(Test::Unit::AssertionFailedError)
+      Test::Unit::AssertionFailedError = MiniTest::Assertion
+    end
+
     # Returns the output of running cmd, and asserts the exit status
     def shell_output(cmd, result = 0)
       ohai cmd