diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 84b01cf84a2ea..0b1d4058e2505 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -66,7 +66,9 @@ class << self
         def new_client(conn_params)
           PG.connect(**conn_params)
         rescue ::PG::Error => error
-          if conn_params && conn_params[:dbname] && error.message.include?(conn_params[:dbname])
+          if conn_params && conn_params[:dbname] == "postgres"
+            raise ActiveRecord::ConnectionNotEstablished, error.message
+          elsif conn_params && conn_params[:dbname] && error.message.include?(conn_params[:dbname])
             raise ActiveRecord::NoDatabaseError.db_error(conn_params[:dbname])
           elsif conn_params && conn_params[:user] && error.message.include?(conn_params[:user])
             raise ActiveRecord::DatabaseConnectionError.username_error(conn_params[:user])
diff --git a/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
index 1a14a89582f97..1fd4b6c88cd40 100644
--- a/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
@@ -78,6 +78,18 @@ def test_bad_connection
         end
       end
 
+      def test_bad_connection_to_postgres_database
+        connect_raises_error = proc { |**_conn_params| raise(PG::ConnectionBad, 'FATAL:  database "postgres" does not exist') }
+        PG.stub(:connect, connect_raises_error) do
+          assert_raises ActiveRecord::ConnectionNotEstablished do
+            db_config = ActiveRecord::Base.configurations.configs_for(env_name: "arunit", name: "primary")
+            configuration = db_config.configuration_hash.merge(database: "postgres")
+            connection = ActiveRecord::Base.postgresql_connection(configuration)
+            connection.exec_query("SELECT 1")
+          end
+        end
+      end
+
       def test_database_exists_returns_false_when_the_database_does_not_exist
         config = { database: "non_extant_database", adapter: "postgresql" }
         assert_not ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.database_exists?(config),