diff --git a/activerecord/CHANGELOG b/activerecord/CHANGELOG
index 5c5b15e33a..d7277a39ec 100644
--- a/activerecord/CHANGELOG
+++ b/activerecord/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Reveal that the type option in migrations can be any supported column type for your database but also include caveat about agnosticism. Closes #7531 [adamwiggins, mikong]
+
 * More complete documentation for find_by_sql. Closes #7912 [fearoffish]
 
 * Document API for exists?'s parameter and provide examples of usage. Closes #7913 [fearoffish]
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index 86ff16531f..2aa8a12228 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -292,12 +292,17 @@ module ActiveRecord
       end
 
       # Instantiates a new column for the table.
-      # The +type+ parameter must be one of the following values:
+      # The +type+ parameter is normally one of the migrations native types,
+      # which is one of the following:
       # <tt>:primary_key</tt>, <tt>:string</tt>, <tt>:text</tt>,
       # <tt>:integer</tt>, <tt>:float</tt>, <tt>:decimal</tt>,
       # <tt>:datetime</tt>, <tt>:timestamp</tt>, <tt>:time</tt>,
       # <tt>:date</tt>, <tt>:binary</tt>, <tt>:boolean</tt>.
       #
+      # You may use a type not in this list as long as it is supported by your
+      # database (for example, "polygon" in MySQL), but this will not be database
+      # agnostic and should usually be avoided.
+      #
       # Available options are (none of these exists by default):
       # * <tt>:limit</tt> -
       #   Requests a maximum column length (<tt>:string</tt>, <tt>:text</tt>,