diff --git a/packages/server/src/core/initTRPC.ts b/packages/server/src/core/initTRPC.ts
index 5e515f87220..da73e95a4a5 100644
--- a/packages/server/src/core/initTRPC.ts
+++ b/packages/server/src/core/initTRPC.ts
@@ -11,7 +11,7 @@ import {
   defaultTransformer,
   getDataTransformer,
 } from '../transformer';
-import { FlatOverwrite, Unwrap } from '../types';
+import { Unwrap } from '../types';
 import {
   CreateRootConfigTypes,
   isServerDefault,
@@ -21,7 +21,7 @@ import {
 } from './internals/config';
 import { mergeRouters } from './internals/mergeRouters';
 import { createBuilder } from './internals/procedureBuilder';
-import { PickFirstDefined, ValidateShape } from './internals/utils';
+import { Overwrite, PickFirstDefined, ValidateShape } from './internals/utils';
 import { createMiddlewareFactory } from './middleware';
 import { createRouterFactory } from './router';
 
@@ -50,13 +50,13 @@ class TRPCBuilder<TParams extends PartialRootConfigTypes = object> {
       | RootConfigTypes['ctx']
       | ((...args: unknown[]) => RootConfigTypes['ctx']),
   >() {
-    type NextParams = FlatOverwrite<TParams, { ctx: Unwrap<TNewContext> }>;
+    type NextParams = Overwrite<TParams, { ctx: Unwrap<TNewContext> }>;
 
     return new TRPCBuilder<NextParams>();
   }
 
   meta<TNewMeta extends RootConfigTypes['meta']>() {
-    type NextParams = FlatOverwrite<TParams, { meta: TNewMeta }>;
+    type NextParams = Overwrite<TParams, { meta: TNewMeta }>;
 
     return new TRPCBuilder<NextParams>();
   }
diff --git a/packages/server/src/core/internals/procedureBuilder.ts b/packages/server/src/core/internals/procedureBuilder.ts
index 28454987da7..c49fec6adac 100644
--- a/packages/server/src/core/internals/procedureBuilder.ts
+++ b/packages/server/src/core/internals/procedureBuilder.ts
@@ -21,7 +21,7 @@ import { AnyRootConfig } from './config';
 import { getParseFn } from './getParseFn';
 import { mergeWithoutOverrides } from './mergeWithoutOverrides';
 import {
-  DefaultValue as FallbackValue,
+  DefaultValue,
   middlewareMarker,
   Overwrite,
   OverwriteKnown,
@@ -40,8 +40,8 @@ type CreateProcedureReturnInput<
   _input_out: UnsetMarker extends TNext['_input_out']
     ? TPrev['_input_out']
     : Overwrite<TPrev['_input_out'], TNext['_input_out']>;
-  _output_in: FallbackValue<TNext['_output_in'], TPrev['_output_in']>;
-  _output_out: FallbackValue<TNext['_output_out'], TPrev['_output_out']>;
+  _output_in: DefaultValue<TNext['_output_in'], TPrev['_output_in']>;
+  _output_out: DefaultValue<TNext['_output_out'], TPrev['_output_out']>;
 }>;
 
 /**
@@ -156,7 +156,7 @@ export interface ProcedureBuilder<TParams extends ProcedureParams> {
   query<$Output>(
     resolver: (
       opts: ResolveOptions<TParams>,
-    ) => MaybePromise<FallbackValue<TParams['_output_in'], $Output>>,
+    ) => MaybePromise<DefaultValue<TParams['_output_in'], $Output>>,
   ): BuildProcedure<'query', TParams, $Output>;
 
   /**
@@ -165,7 +165,7 @@ export interface ProcedureBuilder<TParams extends ProcedureParams> {
   mutation<$Output>(
     resolver: (
       opts: ResolveOptions<TParams>,
-    ) => MaybePromise<FallbackValue<TParams['_output_in'], $Output>>,
+    ) => MaybePromise<DefaultValue<TParams['_output_in'], $Output>>,
   ): BuildProcedure<'mutation', TParams, $Output>;
 
   /**
@@ -174,7 +174,7 @@ export interface ProcedureBuilder<TParams extends ProcedureParams> {
   subscription<$Output>(
     resolver: (
       opts: ResolveOptions<TParams>,
-    ) => MaybePromise<FallbackValue<TParams['_output_in'], $Output>>,
+    ) => MaybePromise<DefaultValue<TParams['_output_in'], $Output>>,
   ): BuildProcedure<'subscription', TParams, $Output>;
   /**
    * @internal
diff --git a/packages/server/src/core/middleware.ts b/packages/server/src/core/middleware.ts
index 5f187192ea6..b2177581cb2 100644
--- a/packages/server/src/core/middleware.ts
+++ b/packages/server/src/core/middleware.ts
@@ -4,7 +4,7 @@ import { AnyRootConfig, RootConfig } from './internals/config';
 import { ParseFn } from './internals/getParseFn';
 import { ProcedureBuilderMiddleware } from './internals/procedureBuilder';
 import {
-  DefaultValue as FallbackValue,
+  DefaultValue,
   MiddlewareMarker,
   Overwrite,
   UnsetMarker,
@@ -64,10 +64,10 @@ export interface MiddlewareBuilder<
       _config: TRoot['_config'];
       _meta: TRoot['_meta'];
       _ctx_out: Overwrite<TRoot['_ctx_out'], TNewParams['_ctx_out']>;
-      _input_in: FallbackValue<TRoot['_input_in'], TNewParams['_input_in']>;
-      _input_out: FallbackValue<TRoot['_input_out'], TNewParams['_input_out']>;
-      _output_in: FallbackValue<TRoot['_output_in'], TNewParams['_output_in']>;
-      _output_out: FallbackValue<
+      _input_in: DefaultValue<TRoot['_input_in'], TNewParams['_input_in']>;
+      _input_out: DefaultValue<TRoot['_input_out'], TNewParams['_input_out']>;
+      _output_in: DefaultValue<TRoot['_output_in'], TNewParams['_output_in']>;
+      _output_out: DefaultValue<
         TRoot['_output_out'],
         TNewParams['_output_out']
       >;
@@ -102,10 +102,10 @@ type CreateMiddlewareReturnInput<
     _config: TPrev['_config'];
     _meta: TPrev['_meta'];
     _ctx_out: Overwrite<TPrev['_ctx_out'], TNext['_ctx_out']>;
-    _input_in: FallbackValue<TNext['_input_in'], TPrev['_input_in']>;
-    _input_out: FallbackValue<TNext['_input_out'], TPrev['_input_out']>;
-    _output_in: FallbackValue<TNext['_output_in'], TPrev['_output_in']>;
-    _output_out: FallbackValue<TNext['_output_out'], TPrev['_output_out']>;
+    _input_in: DefaultValue<TNext['_input_in'], TPrev['_input_in']>;
+    _input_out: DefaultValue<TNext['_input_out'], TPrev['_input_out']>;
+    _output_in: DefaultValue<TNext['_output_in'], TPrev['_output_in']>;
+    _output_out: DefaultValue<TNext['_output_out'], TPrev['_output_out']>;
   }
 >;
 
diff --git a/packages/server/src/types.ts b/packages/server/src/types.ts
index 8b4cbe4e782..f94888a8e08 100644
--- a/packages/server/src/types.ts
+++ b/packages/server/src/types.ts
@@ -1,20 +1,28 @@
 /**
  * @internal
+ * @deprecated
  */
 export type identity<TType> = TType;
 
+/**
+ * @deprecated
+ */
 export type InferOptional<TType, TKeys extends keyof TType> = Omit<
   TType,
   TKeys
 > &
   Partial<Pick<TType, TKeys>>;
 
+/**
+ * @deprecated
+ */
 export type UndefinedKeys<TType> = {
   [K in keyof TType]: undefined extends TType[K] ? K : never;
 }[keyof TType];
 
 /**
  * @internal
+ * @deprecated
  */
 export type FlatOverwrite<TType, TWith> = InferOptional<
   {
diff --git a/packages/tests/server/adapters/fastify.test.ts b/packages/tests/server/adapters/fastify.test.ts
index acd5fc73742..c01272b4dc3 100644
--- a/packages/tests/server/adapters/fastify.test.ts
+++ b/packages/tests/server/adapters/fastify.test.ts
@@ -247,18 +247,20 @@ describe('anonymous user', () => {
     await app.stop();
   });
 
-  test('fetch POST', async () => {
-    const data = { text: 'life', life: 42 };
-    const req = await fetch(`http://localhost:${config.port}/hello`, {
-      method: 'POST',
-      headers: {
-        Accept: 'application/json',
-        'Content-Type': 'application/json',
-      },
-      body: JSON.stringify(data),
-    });
-    // body should be object
-    expect(await req.json()).toMatchInlineSnapshot(`
+  test(
+    'fetch POST',
+    async () => {
+      const data = { text: 'life', life: 42 };
+      const req = await fetch(`http://localhost:${config.port}/hello`, {
+        method: 'POST',
+        headers: {
+          Accept: 'application/json',
+          'Content-Type': 'application/json',
+        },
+        body: JSON.stringify(data),
+      });
+      // body should be object
+      expect(await req.json()).toMatchInlineSnapshot(`
       Object {
         "body": Object {
           "life": 42,
@@ -267,7 +269,11 @@ describe('anonymous user', () => {
         "hello": "POST",
       }
     `);
-  });
+    },
+    {
+      retry: 3,
+    },
+  );
 
   test('query', async () => {
     expect(await app.client.ping.query()).toMatchInlineSnapshot(`"pong"`);