diff --git a/README.md b/README.md
index 69ef4e89..808f13fe 100644
--- a/README.md
+++ b/README.md
@@ -981,6 +981,9 @@ class AddAndDouble < ActiveInteraction::Base
 end
 ```
 
+Note that errors in composed interactions have a few tricky cases. See [the
+errors section][] for more information about them.
+
 ### Defaults
 
 The default value for an input can take on many different forms. Setting the
@@ -1100,6 +1103,42 @@ class UpdateThing < ActiveInteraction::Base
 end
 ```
 
+When a composed interaction fails, its errors are merged onto the caller. This
+generally produces good error messages, but there are a few cases to look out
+for.
+
+``` rb
+class Inner < ActiveInteraction::Base
+  boolean :x, :y
+end
+
+class Outer < ActiveInteraction::Base
+  string :x
+  boolean :z, default: nil
+
+  def execute
+    compose(Inner, x: x, y: z)
+  end
+end
+
+outcome = Outer.run(x: 'yes')
+outcome.errors.details
+# => { :x    => [{ :error => :invalid_type, :type => "boolean" }],
+#      :base => [{ :error => "Y is required" }] }
+outcome.errors.full_messages.join(' and ')
+# => "X is not a valid boolean and Y is required"
+```
+
+Since both interactions have an input called `x`, the inner error for that
+input is moved to the `x` error on the outer interaction. This results in a
+misleading error that claims the input `x` is not a valid boolean even though
+it's a string on the outer interaction.
+
+Since only the inner interaction has an input called `y`, the inner error for
+that input is moved to the `base` error on the outer interaction. This results
+in a confusing error that claims the input `y` is required even though it's not
+present on the outer interaction.
+
 ### Forms
 
 The outcome returned by `.run` can be used in forms as though it were an
@@ -1348,6 +1387,7 @@ ActiveInteraction is licensed under [the MIT License][].
 [formtastic]: https://rubygems.org/gems/formtastic
 [simple_form]: https://rubygems.org/gems/simple_form
 [the filters section]: #filters
+[the errors section]: #errors
 [the optional inputs section]: #optional-inputs
 [aire]: example
 [`with_options`]: http://api.rubyonrails.org/classes/Object.html#method-i-with_options
diff --git a/lib/active_interaction/concerns/runnable.rb b/lib/active_interaction/concerns/runnable.rb
index 04a3b475..fb457cd2 100644
--- a/lib/active_interaction/concerns/runnable.rb
+++ b/lib/active_interaction/concerns/runnable.rb
@@ -80,18 +80,12 @@ def run
 
       self.result =
         if result_or_errors.is_a?(ActiveInteraction::Errors)
-          merge_errors_onto_base(result_or_errors)
+          errors.merge!(result_or_errors)
         else
           result_or_errors
         end
     end
 
-    def merge_errors_onto_base(new_errors)
-      new_errors.full_messages.each do |message|
-        errors.add(:base, message) unless errors.added?(:base, message)
-      end
-    end
-
     # @return [Object]
     #
     # @raise [InvalidInteractionError] If there are validation errors.
diff --git a/lib/active_interaction/errors.rb b/lib/active_interaction/errors.rb
index 150f476a..89889ae5 100644
--- a/lib/active_interaction/errors.rb
+++ b/lib/active_interaction/errors.rb
@@ -97,6 +97,10 @@ def merge!(other)
     def merge_messages!(other)
       other.messages.each do |attribute, messages|
         messages.each do |message|
+          unless attribute?(attribute)
+            message = full_message(attribute, message)
+            attribute = :base
+          end
           add(attribute, message) unless added?(attribute, message)
         end
       end
@@ -107,9 +111,25 @@ def merge_details!(other)
         details.each do |detail|
           detail = detail.dup
           error = detail.delete(:error)
-          add(attribute, error, detail) unless added?(attribute, error, detail)
+
+          merge_detail!(other, attribute, detail, error)
         end
       end
     end
+
+    def merge_detail!(other, attribute, detail, error)
+      if attribute?(attribute)
+        add(attribute, error, detail) unless added?(attribute, error, detail)
+      else
+        message = full_message(
+          attribute, other.generate_message(attribute, error))
+        attribute = :base
+        add(attribute, message) unless added?(attribute, message)
+      end
+    end
+
+    def attribute?(attribute)
+      @base.respond_to?(attribute)
+    end
   end
 end
diff --git a/spec/active_interaction/base_spec.rb b/spec/active_interaction/base_spec.rb
index 1ffafe6e..c0ec9eed 100644
--- a/spec/active_interaction/base_spec.rb
+++ b/spec/active_interaction/base_spec.rb
@@ -19,12 +19,12 @@ def execute
 end
 
 InterruptInteraction = Class.new(TestInteraction) do
-  object :x, :y,
+  object :x, :z,
     class: Object,
     default: nil
 
   def execute
-    compose(AddInteraction, inputs)
+    compose(AddInteraction, x: x, y: z)
   end
 end
 
@@ -337,11 +337,11 @@ def execute
   describe '#compose' do
     let(:described_class) { InterruptInteraction }
     let(:x) { rand }
-    let(:y) { rand }
+    let(:z) { rand }
 
     context 'with valid composition' do
       before do
-        inputs.merge!(x: x, y: y)
+        inputs.merge!(x: x, z: z)
       end
 
       it 'is valid' do
@@ -349,7 +349,7 @@ def execute
       end
 
       it 'returns the sum' do
-        expect(result).to eql x + y
+        expect(result).to eql x + z
       end
     end
 
@@ -359,8 +359,8 @@ def execute
       end
 
       it 'has the correct errors' do
-        expect(outcome.errors[:base])
-          .to match_array ['X is required', 'Y is required']
+        expect(outcome.errors.details)
+          .to eql(x: [{ error: :missing }], base: [{ error: 'Y is required' }])
       end
     end
   end