diff --git a/lib/active_record/migrations/tasks.rb b/lib/active_record/migrations/tasks.rb
index 6732d9d..d5a03e5 100644
--- a/lib/active_record/migrations/tasks.rb
+++ b/lib/active_record/migrations/tasks.rb
@@ -42,7 +42,7 @@ module Tasks
 			module DatabaseTasks
 				def each_current_configuration(environment, spec_name = nil)
 					unless configuration = ActiveRecord::Base.configurations[environment]
-						raise ArgumentError.new("Cannot find configuration for environment #{environment.inspect} in #{ActiveRecord::Base.configurations.keys}")
+						raise ArgumentError.new("Cannot find configuration for environment #{environment.inspect} in #{ActiveRecord::Base.configurations.to_h.keys}")
 					end
 					
 					# This is a hack because DatabaseTasks functionality uses string for keys.
diff --git a/spec/active_record/migrations_spec.rb b/spec/active_record/migrations_spec.rb
index 0ae95ae..c49847d 100644
--- a/spec/active_record/migrations_spec.rb
+++ b/spec/active_record/migrations_spec.rb
@@ -53,4 +53,14 @@
 			expect(File.read('db/schema.rb')).to include("version: 2016_12_08_121932")
 		end
 	end
+	
+	it "should handle non-existent configuration" do
+		require 'active_record/migrations/tasks'
+		ActiveRecord::Base.configurations = {
+			"development" => "null://test",
+		}
+		expect do
+			ActiveRecord::Tasks::DatabaseTasks.send(:each_current_configuration, "foo")
+		end.to raise_error(ArgumentError, 'Cannot find configuration for environment "foo" in ["development"]')
+	end
 end