diff --git a/src/config.ts b/src/config.ts
index 46b9278..343ece2 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -621,6 +621,13 @@ export function normalizeAutoCaptureMaxContextBytes(value: number): number {
   return value;
 }
 
+export function normalizeAutoCleanupRetentionDays(value: number): number {
+  if (!Number.isSafeInteger(value) || value <= 0) {
+    throw new Error(`Invalid autoCleanupRetentionDays config: ${value}`);
+  }
+  return value;
+}
+
 function buildConfig(fileConfig: OpenCodeMemConfig) {
   const memoryApiKey = resolveSecretValue(fileConfig.memoryApiKey);
   const embeddingDimensions =
@@ -697,8 +704,9 @@ function buildConfig(fileConfig: OpenCodeMemConfig) {
       : undefined,
     maxVectorsPerShard: fileConfig.maxVectorsPerShard ?? DEFAULTS.maxVectorsPerShard,
     autoCleanupEnabled: fileConfig.autoCleanupEnabled ?? DEFAULTS.autoCleanupEnabled,
-    autoCleanupRetentionDays:
-      fileConfig.autoCleanupRetentionDays ?? DEFAULTS.autoCleanupRetentionDays,
+    autoCleanupRetentionDays: normalizeAutoCleanupRetentionDays(
+      fileConfig.autoCleanupRetentionDays ?? DEFAULTS.autoCleanupRetentionDays
+    ),
     deduplicationEnabled: fileConfig.deduplicationEnabled ?? DEFAULTS.deduplicationEnabled,
     deduplicationSimilarityThreshold:
       fileConfig.deduplicationSimilarityThreshold ?? DEFAULTS.deduplicationSimilarityThreshold,
@@ -845,7 +853,10 @@ export function initConfig(directory: string): void {
   const globalConfig = loadConfigFromPaths(CONFIG_FILES);
   const projectConfig = loadConfigFromPaths(projectPaths);
   assertProjectRemoteProviderConfigIsSafe(projectConfig);
-  const merged: OpenCodeMemConfig = { ...globalConfig, ...projectConfig };
+  const projectOverrides = { ...projectConfig };
+  delete projectOverrides.autoCleanupEnabled;
+  delete projectOverrides.autoCleanupRetentionDays;
+  const merged: OpenCodeMemConfig = { ...globalConfig, ...projectOverrides };
   CONFIG = buildConfig(merged);
 }
 
diff --git a/tests/config-resolution.test.ts b/tests/config-resolution.test.ts
index 7e88e3c..fcdc771 100644
--- a/tests/config-resolution.test.ts
+++ b/tests/config-resolution.test.ts
@@ -47,6 +47,48 @@ describe("project-scoped config resolution", () => {
     expect(CONFIG.opencodeModel).toBe("project-model");
   });
 
+  it("keeps automatic cleanup policy under global configuration", () => {
+    existsSpy = spyOn(fs, "existsSync").mockReturnValue(true);
+    readSpy = spyOn(fs, "readFileSync").mockImplementation((p) => {
+      const path = normalizePath(p);
+      if (path.includes(".opencode/opencode-mem")) {
+        return JSON.stringify({
+          opencodeModel: "project-model",
+          autoCleanupEnabled: true,
+          autoCleanupRetentionDays: 0,
+        }) as any;
+      }
+      return JSON.stringify({
+        opencodeModel: "global-model",
+        autoCleanupEnabled: false,
+        autoCleanupRetentionDays: 90,
+      }) as any;
+    });
+
+    initConfig("/my/project");
+
+    expect(CONFIG.opencodeModel).toBe("project-model");
+    expect(CONFIG.autoCleanupEnabled).toBe(false);
+    expect(CONFIG.autoCleanupRetentionDays).toBe(90);
+  });
+
+  it("uses safe cleanup defaults when only project cleanup settings exist", () => {
+    existsSpy = spyOn(fs, "existsSync").mockImplementation((p) =>
+      normalizePath(p).includes("/my/project/.opencode/opencode-mem")
+    );
+    readSpy = spyOn(fs, "readFileSync").mockReturnValue(
+      JSON.stringify({
+        autoCleanupEnabled: true,
+        autoCleanupRetentionDays: -1,
+      })
+    );
+
+    initConfig("/my/project");
+
+    expect(CONFIG.autoCleanupEnabled).toBe(true);
+    expect(CONFIG.autoCleanupRetentionDays).toBe(30);
+  });
+
   it("rejects project embedding transport settings before they can inherit secrets", () => {
     const oldOpenAiKey = process.env.OPENAI_API_KEY;
     process.env.OPENAI_API_KEY = "ambient-secret";
diff --git a/tests/config.test.ts b/tests/config.test.ts
index 3438710..f1304a2 100644
--- a/tests/config.test.ts
+++ b/tests/config.test.ts
@@ -15,6 +15,7 @@ const {
   hasAutoCaptureProviderConfig,
   isConfigured,
   isPlaceholderApiKey,
+  normalizeAutoCleanupRetentionDays,
   normalizeAutoCaptureMaxContextBytes,
 } = await import("../src/config.js");
 
@@ -99,6 +100,15 @@ describe("config", () => {
       expect(() => normalizeAutoCaptureMaxContextBytes(16 * 1024 * 1024 + 1)).toThrow();
     });
 
+    it("should reject unsafe automatic cleanup retention periods", () => {
+      expect(() => normalizeAutoCleanupRetentionDays(0)).toThrow();
+      expect(() => normalizeAutoCleanupRetentionDays(-1)).toThrow();
+      expect(() => normalizeAutoCleanupRetentionDays(1.5)).toThrow();
+      expect(() => normalizeAutoCleanupRetentionDays(Number.POSITIVE_INFINITY)).toThrow();
+      expect(normalizeAutoCleanupRetentionDays(1)).toBe(1);
+      expect(normalizeAutoCleanupRetentionDays(30)).toBe(30);
+    });
+
     it("should expose memory scope config", () => {
       const defaultScope = CONFIG.memory.defaultScope ?? "project";
       expect(["project", "all-projects"]).toContain(defaultScope);