diff --git a/apps/content/docs/openapi/input-output-structure.md b/apps/content/docs/openapi/input-output-structure.md
index 8b5fa2bbd..2a05a8521 100644
--- a/apps/content/docs/openapi/input-output-structure.md
+++ b/apps/content/docs/openapi/input-output-structure.md
@@ -13,7 +13,7 @@ The `inputStructure` option defines how the incoming request data is structured.
 
 ### Compact Mode (default)
 
-Combines path parameters with query or body data (depending on the HTTP method) into a single object.
+Combines path parameters with query or body data (depending on the HTTP method) into a single object. Path parameters take precedence over query or body fields with the same name. If the path has parameters and the body cannot be merged (e.g. a primitive, array, or file), only the path parameters are used. Use detailed mode if you also need the body.
 
 ```ts
 const compactMode = os.route({
diff --git a/packages/openapi/src/adapters/fetch/openapi-handler.test.ts b/packages/openapi/src/adapters/fetch/openapi-handler.test.ts
index 119b90e7a..e9bfe99ed 100644
--- a/packages/openapi/src/adapters/fetch/openapi-handler.test.ts
+++ b/packages/openapi/src/adapters/fetch/openapi-handler.test.ts
@@ -12,4 +12,23 @@ describe('openAPIHandler', () => {
     await expect(response?.text()).resolves.toContain('hello')
     expect(response?.status).toBe(200)
   })
+
+  it('does not let query or body override path params in compact input', async () => {
+    const handler = new OpenAPIHandler({
+      get: os.route({ method: 'GET', path: '/posts/{id}' }).handler(({ input }) => input),
+      update: os.route({ method: 'POST', path: '/posts/{id}' }).handler(({ input }) => input),
+    })
+
+    const { response: getResponse } = await handler.handle(new Request('https://example.com/posts/42?id=99&q=hello'))
+
+    await expect(getResponse?.json()).resolves.toEqual({ id: '42', q: 'hello' })
+
+    const { response: postResponse } = await handler.handle(new Request('https://example.com/posts/24', {
+      method: 'POST',
+      headers: { 'content-type': 'application/json' },
+      body: JSON.stringify({ id: '99', title: 'hello' }),
+    }))
+
+    await expect(postResponse?.json()).resolves.toEqual({ id: '24', title: 'hello' })
+  })
 })
diff --git a/packages/openapi/src/adapters/standard/openapi-codec.test.ts b/packages/openapi/src/adapters/standard/openapi-codec.test.ts
index f85040977..587771e26 100644
--- a/packages/openapi/src/adapters/standard/openapi-codec.test.ts
+++ b/packages/openapi/src/adapters/standard/openapi-codec.test.ts
@@ -74,6 +74,92 @@ describe('standardOpenAPICodec', () => {
         expect(serializer.deserialize).toHaveBeenCalledOnce()
         expect(serializer.deserialize).toHaveBeenCalledWith(serialized)
       })
+
+      it('gives path params precedence over conflicting query params', async () => {
+        serializer.deserialize.mockReturnValueOnce({ id: '99', q: 'hello' })
+
+        const input = await codec.decode({
+          method: 'GET',
+          url: new URL('http://localhost/42?id=99&q=hello'),
+          body: vi.fn(),
+          headers: {},
+          signal: undefined,
+        }, { id: '42' }, ping)
+
+        expect(input).toEqual({ id: '42', q: 'hello' })
+      })
+
+      it('gives path params precedence over conflicting body properties', async () => {
+        serializer.deserialize.mockReturnValueOnce({ id: '99', title: 'hello' })
+
+        const input = await codec.decode({
+          method: 'POST',
+          url: new URL('http://localhost/24'),
+          body: vi.fn(async () => '__body__'),
+          headers: {},
+          signal: undefined,
+        }, { id: '24' }, ping)
+
+        expect(input).toEqual({ id: '24', title: 'hello' })
+      })
+
+      it('returns only path params when a primitive body cannot be merged', async () => {
+        serializer.deserialize.mockReturnValueOnce('raw-body')
+
+        const input = await codec.decode({
+          method: 'POST',
+          url: new URL('http://localhost/24'),
+          body: vi.fn(async () => '__body__'),
+          headers: {},
+          signal: undefined,
+        }, { id: '24' }, ping)
+
+        expect(input).toEqual({ id: '24' })
+      })
+
+      it('returns only path params when an array body cannot be merged', async () => {
+        serializer.deserialize.mockReturnValueOnce(['first', 'second'])
+
+        const input = await codec.decode({
+          method: 'POST',
+          url: new URL('http://localhost/24'),
+          body: vi.fn(async () => '__body__'),
+          headers: {},
+          signal: undefined,
+        }, { id: '24' }, ping)
+
+        expect(input).toEqual({ id: '24' })
+      })
+
+      it('returns only path params when a binary body cannot be merged', async () => {
+        const file = new File(['raw-bytes'], 'other.txt')
+        serializer.deserialize.mockReturnValueOnce(file)
+
+        const input = await codec.decode({
+          method: 'POST',
+          url: new URL('http://localhost/report.txt'),
+          body: vi.fn(async () => file),
+          headers: {},
+          signal: undefined,
+        }, { name: 'report.txt' }, ping)
+
+        expect(input).toEqual({ name: 'report.txt' })
+      })
+
+      it('returns a binary body as-is when there are no path params', async () => {
+        const blob = new Blob(['raw-bytes'])
+        serializer.deserialize.mockReturnValueOnce(blob)
+
+        const input = await codec.decode({
+          method: 'POST',
+          url: new URL('http://localhost/submit'),
+          body: vi.fn(async () => blob),
+          headers: {},
+          signal: undefined,
+        }, undefined, ping)
+
+        expect(input).toBe(blob)
+      })
     })
 
     describe('with detailed structure', () => {
diff --git a/packages/openapi/src/adapters/standard/openapi-codec.ts b/packages/openapi/src/adapters/standard/openapi-codec.ts
index 9b719f557..484c84d37 100644
--- a/packages/openapi/src/adapters/standard/openapi-codec.ts
+++ b/packages/openapi/src/adapters/standard/openapi-codec.ts
@@ -42,14 +42,20 @@ export class StandardOpenAPICodec implements StandardCodec {
         return params
       }
 
-      if (isObject(data)) {
-        return {
-          ...params,
-          ...data,
-        }
+      if (!params || Object.keys(params).length < 1) {
+        return data
       }
 
-      return data
+      // Non-object data (primitive, array, Blob, ReadableStream, ...) cannot be merged with params.
+      // Prefer params to stay consistent with the OpenAPI generator, which only describes path params here.
+      if (!isObject(data)) {
+        return params
+      }
+
+      return {
+        ...data,
+        ...params,
+      }
     }
 
     const deserializeSearchParams = () => {