diff --git a/activesupport/lib/active_support/dependencies.rb b/activesupport/lib/active_support/dependencies.rb
index 5dbe466b7b3d2276dff73da1838e09d56377c844..67620e178966f01fd266ebc9e4c43b2ef533f0e6 100644
--- a/activesupport/lib/active_support/dependencies.rb
+++ b/activesupport/lib/active_support/dependencies.rb
@@ -485,24 +485,28 @@ def new_constants_in(*descs)
       # Build the watch frames. Each frame is a tuple of
       #   [module_name_as_string, constants_defined_elsewhere]
       watch_frames = descs.collect do |desc|
-        if desc.is_a? Module
-          mod_name = desc.name
-          initial_constants = desc.local_constant_names
-        elsif desc.is_a?(String) || desc.is_a?(Symbol)
-          mod_name = desc.to_s
-
-          # Handle the case where the module has yet to be defined.
-          initial_constants = if qualified_const_defined?(mod_name)
-            mod_name.constantize.local_constant_names
+        begin
+          if desc.is_a? Module
+            mod_name = desc.name
+            initial_constants = desc.local_constant_names
+          elsif desc.is_a?(String) || desc.is_a?(Symbol)
+            mod_name = desc.to_s
+
+            # Handle the case where the module has yet to be defined.
+            initial_constants = if qualified_const_defined?(mod_name)
+              mod_name.constantize.local_constant_names
+            else
+              []
+            end
           else
-           []
+            raise Argument, "#{desc.inspect} does not describe a module!"
           end
-        else
-          raise Argument, "#{desc.inspect} does not describe a module!"
+          [mod_name, initial_constants]
+        rescue NameError
+          # mod_name isn't a valid constant name
+          nil
         end
-
-        [mod_name, initial_constants]
-      end
+      end.compact
 
       constant_watch_stack.concat watch_frames
 
diff --git a/railties/lib/initializer.rb b/railties/lib/initializer.rb
index 3e97a17e0ec9a103e7d63bfc430b8585324bc63a..16abe62d1b03e78c59e574e143c0d19c65f68ec4 100644
--- a/railties/lib/initializer.rb
+++ b/railties/lib/initializer.rb
@@ -901,6 +901,7 @@ def default_load_paths
           components
           config
           lib
+          vendor
         ).map { |dir| "#{root_path}/#{dir}" }.select { |dir| File.directory?(dir) }
 
         paths.concat builtin_directories