diff --git a/lib/shoulda/matchers.rb b/lib/shoulda/matchers.rb
index 3786927a..910a7fc5 100644
--- a/lib/shoulda/matchers.rb
+++ b/lib/shoulda/matchers.rb
@@ -3,6 +3,7 @@ require 'shoulda/matchers/doublespeak'
 require 'shoulda/matchers/error'
 require 'shoulda/matchers/matcher_context'
 require 'shoulda/matchers/rails_shim'
+require 'shoulda/matchers/util'
 require 'shoulda/matchers/version'
 require 'shoulda/matchers/warn'
 
diff --git a/lib/shoulda/matchers/util.rb b/lib/shoulda/matchers/util.rb
new file mode 100644
index 00000000..d14ef6cc
--- /dev/null
+++ b/lib/shoulda/matchers/util.rb
@@ -0,0 +1,15 @@
+module Shoulda
+  module Matchers
+    # @private
+    module Util
+      def self.deconstantize(path)
+        if defined?(ActiveSupport::Inflector) &&
+          ActiveSupport::Inflector.respond_to?(:deconstantize)
+          ActiveSupport::Inflector.deconstantize(path)
+        else
+          path.to_s[0...(path.to_s.rindex('::') || 0)]
+        end
+      end
+    end
+  end
+end
diff --git a/spec/support/class_builder.rb b/spec/support/class_builder.rb
index 67833854..41a002e5 100644
--- a/spec/support/class_builder.rb
+++ b/spec/support/class_builder.rb
@@ -7,31 +7,37 @@ module ClassBuilder
     end
   end
 
-  def define_class(class_name, base = Object, &block)
+  def self.parse_constant_name(name)
+    namespace = Shoulda::Matchers::Util.deconstantize(name)
+    qualified_namespace = (namespace.presence || 'Object').constantize
+    name_without_namespace = name.to_s.demodulize
+    [qualified_namespace, name_without_namespace]
+  end
+
+  def define_class(class_name, parent_class = Object, &block)
     class_name = class_name.to_s.camelize
 
-    if Object.const_defined?(class_name)
-      Object.__send__(:remove_const, class_name)
+    namespace, name_without_namespace =
+      ClassBuilder.parse_constant_name(class_name)
+
+    if namespace.const_defined?(name_without_namespace, false)
+      namespace.__send__(:remove_const, name_without_namespace)
     end
 
-    # FIXME: ActionMailer 3.2 calls `name.underscore` immediately upon
-    # subclassing. Class.new.name == nil. So, Class.new(ActionMailer::Base)
-    # errors out since it's trying to do `nil.underscore`. This is very ugly but
-    # allows us to test against ActionMailer 3.2.x.
-    eval <<-A_REAL_CLASS_FOR_ACTION_MAILER_3_2
-    class ::#{class_name} < #{base}
-    end
-    A_REAL_CLASS_FOR_ACTION_MAILER_3_2
+    eval <<-RUBY
+      class #{namespace}::#{name_without_namespace} < #{parent_class}
+      end
+    RUBY
 
-    Object.const_get(class_name).tap do |constant_class|
-      constant_class.unloadable
+    namespace.const_get(name_without_namespace).tap do |constant|
+      constant.unloadable
 
       if block_given?
-        constant_class.class_eval(&block)
+        constant.class_eval(&block)
       end
 
-      if constant_class.respond_to?(:reset_column_information)
-        constant_class.reset_column_information
+      if constant.respond_to?(:reset_column_information)
+        constant.reset_column_information
       end
     end
   end
diff --git a/spec/support/model_builder.rb b/spec/support/model_builder.rb
index 80126fd7..1b6225a1 100644
--- a/spec/support/model_builder.rb
+++ b/spec/support/model_builder.rb
@@ -46,7 +46,8 @@ module ModelBuilder
 
   def define_model(name, columns = {}, &block)
     class_name = name.to_s.pluralize.classify
-    table_name = class_name.tableize
+    table_name = class_name.tableize.gsub('/', '_')
+
     table_block = lambda do |table|
       columns.each do |name, specification|
         if specification.is_a?(Hash)
@@ -64,7 +65,13 @@ module ModelBuilder
       create_table(table_name, &table_block)
     end
 
-    define_model_class(class_name, &block)
+    define_model_class(class_name).tap do |model|
+      if block
+        model.class_eval(&block)
+      end
+
+      model.table_name = table_name
+    end
   end
 
   def drop_created_tables