2 files changed, 14 insertions, 3 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb
index 30ccb8f0a4..2859fb31e8 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb
@@ -17,6 +17,15 @@ module ActiveRecord
         64
       end
 
+      # Returns the maximum allowed length for an index name. This
+      # limit is enforced by rails and Is less than or equal to
+      # <tt>index_name_length</tt>. The gap between
+      # <tt>index_name_length</tt> is to allow internal rails
+      # opreations to use prefixes in temporary opreations.
+      def allowed_index_name_length
+        index_name_length
+      end
+
       # Returns the maximum length of an index name.
       def index_name_length
         64
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index cdc8433185..2c0a18fd01 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -647,10 +647,11 @@ module ActiveRecord
           index_name   = index_name(table_name, column: column_names)
 
           if Hash === options # legacy support, since this param was a string
-            options.assert_valid_keys(:unique, :order, :name, :where, :length)
+            options.assert_valid_keys(:unique, :order, :name, :where, :length, :internal)
 
             index_type = options[:unique] ? "UNIQUE" : ""
             index_name = options[:name].to_s if options.key?(:name)
+            max_index_length = options.fetch(:internal, false) ? index_name_length : allowed_index_name_length
 
             if supports_partial_index?
               index_options = options[:where] ? " WHERE #{options[:where]}" : ""
@@ -665,10 +666,11 @@ module ActiveRecord
             end
 
             index_type = options
+            max_index_length = allowed_index_name_length
           end
 
-          if index_name.length > index_name_length
-            raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' is too long; the limit is #{index_name_length} characters"
+          if index_name.length > max_index_length
+            raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' is too long; the limit is #{max_index_length} characters"
           end
           if index_name_exists?(table_name, index_name, false)
             raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' already exists"