diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb
index 123b3654e68a3204c48286a968773635eaecc776..7312e34f01f510cafa65115e18dee60c8a7d6be9 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb
@@ -54,7 +54,7 @@ def connection
     #
     # The exceptions AdapterNotSpecified, AdapterNotFound and ArgumentError
     # may be returned on an error.
-    def self.establish_connection(spec = nil)
+    def self.establish_connection(spec = ENV["DATABASE_URL"])
       case spec
         when nil
           raise AdapterNotSpecified unless defined?(Rails.env)