diff --git a/Makefile b/Makefile
index de57510..917c050 100644
--- a/Makefile
+++ b/Makefile
@@ -15,7 +15,7 @@ distclean: clean
 	rm -rf node_modules
 
 .PHONY: test
-test: node_modules
+test: node_modules dist
 	pnpm exec vitest
 
 .PHONY: test.update
diff --git a/lib/command.ts b/lib/command.ts
index e7145b2..67bd638 100644
--- a/lib/command.ts
+++ b/lib/command.ts
@@ -3,15 +3,15 @@ import type { JsonifiableObject } from 'type-fest/source/jsonifiable.js';
 import type { HttpMethod } from './types.js';
 
 type Middleware<
-  CommandInput extends JsonifiableObject | undefined,
-  CommandOutput extends Jsonifiable | undefined,
+  CommandInput extends JsonifiableObject | undefined = never,
+  CommandOutput extends Jsonifiable | undefined = never,
 > = (input: CommandInput, output: CommandOutput) => CommandOutput;
 
 export abstract class Command<
-  CommandInput extends JsonifiableObject | undefined,
-  CommandOutput extends Jsonifiable | undefined,
-  CommandBody extends Jsonifiable | undefined,
-  CommandQuery extends JsonifiableObject | undefined,
+  CommandInput extends JsonifiableObject | undefined = never,
+  CommandOutput extends Jsonifiable | undefined = never,
+  CommandBody extends Jsonifiable | undefined = never,
+  CommandQuery extends JsonifiableObject | undefined = never,
 > {
   public method: HttpMethod = 'get';
 
diff --git a/test/test1.test.ts b/test/test1.test.ts
index 144f12e..8f239a9 100644
--- a/test/test1.test.ts
+++ b/test/test1.test.ts
@@ -11,10 +11,10 @@ import {
 import { BillingCountry } from './fixtures/test1/types.js';
 
 async function thisAlwaysThrows<
-  CommandInput extends JsonifiableObject | undefined,
-  CommandOutput extends Jsonifiable | undefined,
-  CommandBody extends Jsonifiable | undefined,
-  CommandQuery extends JsonifiableObject | undefined,
+  CommandInput extends JsonifiableObject | undefined = never,
+  CommandOutput extends Jsonifiable | undefined = never,
+  CommandBody extends Jsonifiable | undefined = never,
+  CommandQuery extends JsonifiableObject | undefined = never,
 >(
   // eslint-disable-next-line @typescript-eslint/no-unused-vars
   _: Command<CommandInput, CommandOutput, CommandBody, CommandQuery>,