1 files changed, 3 insertions, 1 deletions
diff --git a/activemodel/lib/active_model/attribute_methods.rb b/activemodel/lib/active_model/attribute_methods.rb
index 039cd8bdf3..99918fdb96 100644
--- a/activemodel/lib/active_model/attribute_methods.rb
+++ b/activemodel/lib/active_model/attribute_methods.rb
@@ -102,6 +102,7 @@ module ActiveModel
       #   person.name          # => nil
       def attribute_method_prefix(*prefixes)
         self.attribute_method_matchers += prefixes.map { |prefix| AttributeMethodMatcher.new :prefix => prefix }
+        undefine_attribute_methods
       end
 
       # Declares a method available for all attributes with the given suffix.
@@ -138,6 +139,7 @@ module ActiveModel
       #   person.name_short?   # => true
       def attribute_method_suffix(*suffixes)
         self.attribute_method_matchers += suffixes.map { |suffix| AttributeMethodMatcher.new :suffix => suffix }
+        undefine_attribute_methods
       end
 
       # Declares a method available for all attributes with the given prefix
@@ -175,6 +177,7 @@ module ActiveModel
       #   person.name                         # => 'Gemma'
       def attribute_method_affix(*affixes)
         self.attribute_method_matchers += affixes.map { |affix| AttributeMethodMatcher.new :prefix => affix[:prefix], :suffix => affix[:suffix] }
+        undefine_attribute_methods
       end
 
 
@@ -222,7 +225,6 @@ module ActiveModel
       #     end
       #   end
       def define_attribute_methods(*attr_names)
-        undefine_attribute_methods
         attr_names.flatten.each { |attr_name| define_attribute_method(attr_name) }
       end