1 files changed, 9 insertions, 1 deletions
diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb
index 38f37f5c8a..e2b132ca81 100644
--- a/activerecord/lib/active_record/validations/uniqueness.rb
+++ b/activerecord/lib/active_record/validations/uniqueness.rb
@@ -51,7 +51,15 @@ module ActiveRecord
           value = value.attributes[reflection.primary_key_column.name] unless value.nil?
         end
 
-        column = klass.columns_hash[attribute.to_s]
+        attribute_name = attribute.to_s
+
+        # the attribute may be an aliased attribute
+        if klass.attribute_aliases[attribute_name]
+          attribute = klass.attribute_aliases[attribute_name]
+          attribute_name = attribute.to_s
+        end
+
+        column = klass.columns_hash[attribute_name]
         value  = klass.connection.type_cast(value, column)
         value  = value.to_s[0, column.limit] if value && column.limit && column.text?