diff --git a/.changeset/diagnostics-provider-conflicts.md b/.changeset/diagnostics-provider-conflicts.md
new file mode 100644
index 000000000..6b1875f05
--- /dev/null
+++ b/.changeset/diagnostics-provider-conflicts.md
@@ -0,0 +1,5 @@
+---
+"@croco/diagnostics-core": patch
+---
+
+Reject duplicate diagnostics provider names instead of silently overwriting an existing provider.
diff --git a/docs/troubleshooting/diagnostics.md b/docs/troubleshooting/diagnostics.md
index 7e8532184..9d7851d3b 100644
--- a/docs/troubleshooting/diagnostics.md
+++ b/docs/troubleshooting/diagnostics.md
@@ -99,6 +99,9 @@ const app = createApp({
 
 각 `DiagnosticsProvider`는 다음과 같은 정보를 수집합니다.
 
+Provider `name`은 collector 안에서 유일해야 합니다. 같은 인스턴스를 다시 등록하는 것은 no-op이지만,
+같은 `name`을 가진 다른 provider를 등록하면 `DuplicateDiagnosticsProviderProblem`이 발생합니다.
+
 ### TelemetryDiagnosticsProvider
 
 - **수집 정보**: OTel SDK 초기화 여부(`isInitialized`), 현재 샘플링 확률(`probability`)
diff --git a/packages/diagnostics-core/package.json b/packages/diagnostics-core/package.json
index 0f7e38968..bce2ed9e0 100644
--- a/packages/diagnostics-core/package.json
+++ b/packages/diagnostics-core/package.json
@@ -26,6 +26,8 @@
     "test": "vitest run",
     "typecheck": "tsc --noEmit"
   },
-  "dependencies": {},
+  "dependencies": {
+    "@croco/problems-core": "workspace:*"
+  },
   "devDependencies": {}
 }
diff --git a/packages/diagnostics-core/src/index.ts b/packages/diagnostics-core/src/index.ts
index b7608abfc..41ead2c32 100644
--- a/packages/diagnostics-core/src/index.ts
+++ b/packages/diagnostics-core/src/index.ts
@@ -2,6 +2,7 @@
 
 export { DiagnosticsCollector } from "./libs/DiagnosticsCollector";
 export { ErrorHistoryRingBuffer } from "./libs/ErrorHistoryRingBuffer";
+export { DuplicateDiagnosticsProviderProblem } from "./libs/problems/DiagnosticsProblems";
 export type {
   DiagnosticsProvider,
   HealthStatus,
diff --git a/packages/diagnostics-core/src/libs/DiagnosticsCollector.ts b/packages/diagnostics-core/src/libs/DiagnosticsCollector.ts
index 586b36e82..33f3335e7 100644
--- a/packages/diagnostics-core/src/libs/DiagnosticsCollector.ts
+++ b/packages/diagnostics-core/src/libs/DiagnosticsCollector.ts
@@ -1,5 +1,6 @@
 import type { DiagnosticsProvider, HealthStatus, ErrorRecord, DiagnosticsReport } from "./types";
 import { ErrorHistoryRingBuffer } from "./ErrorHistoryRingBuffer";
+import { DuplicateDiagnosticsProviderProblem } from "./problems/DiagnosticsProblems";
 
 function capMessage(message: string, maxLength: number): string {
   if (message.length <= maxLength) {
@@ -26,6 +27,16 @@ export class DiagnosticsCollector {
   private readonly errors = new ErrorHistoryRingBuffer();
 
   registerProvider(provider: DiagnosticsProvider): void {
+    const existingProvider = this.providers.get(provider.name);
+
+    if (existingProvider !== undefined) {
+      if (existingProvider === provider) {
+        return;
+      }
+
+      throw new DuplicateDiagnosticsProviderProblem(provider.name);
+    }
+
     this.providers.set(provider.name, provider);
   }
 
diff --git a/packages/diagnostics-core/src/libs/problems/DiagnosticsProblems.ts b/packages/diagnostics-core/src/libs/problems/DiagnosticsProblems.ts
new file mode 100644
index 000000000..f11f0d009
--- /dev/null
+++ b/packages/diagnostics-core/src/libs/problems/DiagnosticsProblems.ts
@@ -0,0 +1,18 @@
+import { Problem, ProblemCategory } from "@croco/problems-core";
+
+/**
+ * 같은 이름으로 서로 다른 diagnostics provider가 등록될 때 발생하는 Problem입니다.
+ */
+export class DuplicateDiagnosticsProviderProblem extends Problem {
+  readonly code = "diagnostics-core/duplicate-provider";
+  readonly category = ProblemCategory.InternalServerError;
+
+  constructor(providerName: string) {
+    super(undefined, undefined, `Diagnostics provider '${providerName}' is already registered`, {
+      extensions: {
+        providerName,
+        retryable: false,
+      },
+    });
+  }
+}
diff --git a/packages/diagnostics-core/src/tests/DiagnosticsIntegration.spec.ts b/packages/diagnostics-core/src/tests/DiagnosticsIntegration.spec.ts
index e41ccf753..746482a75 100644
--- a/packages/diagnostics-core/src/tests/DiagnosticsIntegration.spec.ts
+++ b/packages/diagnostics-core/src/tests/DiagnosticsIntegration.spec.ts
@@ -1,5 +1,6 @@
 import { beforeEach, describe, expect, it } from "vitest";
 import { DiagnosticsCollector } from "../libs/DiagnosticsCollector";
+import { DuplicateDiagnosticsProviderProblem } from "../libs/problems/DiagnosticsProblems";
 import type { DiagnosticsProvider, HealthStatus, ErrorRecord } from "../libs/types";
 
 class MockDiagnosticsProvider implements DiagnosticsProvider {
@@ -132,6 +133,45 @@ describe("DiagnosticsCollector Integration", () => {
     expect(providers[1].name).toBe("cache");
   });
 
+  it("should keep the original provider when a different provider uses the same name", async () => {
+    const provider1 = new MockDiagnosticsProvider("db", {
+      status: "healthy",
+      component: "db",
+      lastChecked: new Date().toISOString(),
+    });
+    const provider2 = new MockDiagnosticsProvider("db", {
+      status: "unhealthy",
+      component: "db",
+      lastChecked: new Date().toISOString(),
+    });
+
+    collector.registerProvider(provider1);
+
+    expect(() => collector.registerProvider(provider2)).toThrow(
+      DuplicateDiagnosticsProviderProblem,
+    );
+
+    const providers = collector.getProviders();
+    const report = await collector.getReport();
+
+    expect(providers).toEqual([provider1]);
+    expect(report.components).toHaveLength(1);
+    expect(report.components[0].status).toBe("healthy");
+  });
+
+  it("should treat registering the same provider instance as idempotent", () => {
+    const provider = new MockDiagnosticsProvider("db", {
+      status: "healthy",
+      component: "db",
+      lastChecked: new Date().toISOString(),
+    });
+
+    collector.registerProvider(provider);
+    collector.registerProvider(provider);
+
+    expect(collector.getProviders()).toEqual([provider]);
+  });
+
   it("should handle provider that throws in getHealth()", async () => {
     const failingProvider = new MockDiagnosticsProvider("failing-service", {
       status: "healthy",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index d6cf2c2d0..8bd737988 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -648,7 +648,11 @@ importers:
         specifier: 4.0.16
         version: 4.0.16(@opentelemetry/api@1.9.0)(@types/node@25.2.0)(jiti@2.6.1)(tsx@4.21.0)(yaml@2.8.3)
 
-  packages/diagnostics-core: {}
+  packages/diagnostics-core:
+    dependencies:
+      '@croco/problems-core':
+        specifier: workspace:*
+        version: link:../problems-core
 
   packages/docs:
     dependencies: