diff --git a/Library/Homebrew/test/test_exceptions.rb b/Library/Homebrew/test/test_exceptions.rb
index e492017363..88744a2553 100644
--- a/Library/Homebrew/test/test_exceptions.rb
+++ b/Library/Homebrew/test/test_exceptions.rb
@@ -37,6 +37,25 @@ class ExceptionsTest < Homebrew::TestCase
       TapFormulaUnavailableError.new(t, "foo").to_s
   end
 
+  def test_formula_class_unavailable_error
+    mod = Module.new
+    mod.module_eval <<-EOS.undent
+      class Bar < Requirement; end
+      class Baz < Formula; end
+    EOS
+
+    assert_match "Expected to find class Foo, but found no classes.",
+      FormulaClassUnavailableError.new("foo", "foo.rb", "Foo", []).to_s
+
+    list = [mod.const_get(:Bar)]
+    assert_match "Expected to find class Foo, but only found: Bar (not derived from Formula!).",
+      FormulaClassUnavailableError.new("foo", "foo.rb", "Foo", list).to_s
+
+    list = [mod.const_get(:Baz)]
+    assert_match "Expected to find class Foo, but only found: Baz.",
+      FormulaClassUnavailableError.new("foo", "foo.rb", "Foo", list).to_s
+  end
+
   def test_tap_unavailable_error
     assert_equal "No available tap foo.\n", TapUnavailableError.new("foo").to_s
   end
diff --git a/Library/Homebrew/test/test_formulary.rb b/Library/Homebrew/test/test_formulary.rb
index 738012c176..d8f57a90b4 100644
--- a/Library/Homebrew/test/test_formulary.rb
+++ b/Library/Homebrew/test/test_formulary.rb
@@ -54,6 +54,16 @@ class FormularyFactoryTest < Homebrew::TestCase
     assert_raises(FormulaUnavailableError) { Formulary.factory("not_existed_formula") }
   end
 
+  def test_formula_class_unavailable_error
+    name = "giraffe"
+    path = CoreTap.new.formula_dir/"#{name}.rb"
+    path.write "class Wrong#{Formulary.class_s(name)} < Formula\nend\n"
+
+    assert_raises(FormulaClassUnavailableError) { Formulary.factory(name) }
+  ensure
+    path.unlink
+  end
+
   def test_factory_from_path
     assert_kind_of Formula, Formulary.factory(@path)
   end