diff --git a/src/tools/wikis.ts b/src/tools/wikis.ts
index e17b07c..d13a9a8 100644
--- a/src/tools/wikis.ts
+++ b/src/tools/wikis.ts
@@ -48,7 +48,7 @@ export const searchWikiPagesShape = {
     .optional()
     .describe("Substring keyword to match in wiki page title"),
   projectId: z
-    .union([z.string(), z.number()])
+    .union([z.number().int().positive(), z.string().min(1)])
     .optional()
     .describe("Project ID or identifier to scope search"),
   limit: z
diff --git a/tests/tools.test.ts b/tests/tools.test.ts
index f98558b..8c3cebc 100644
--- a/tests/tools.test.ts
+++ b/tests/tools.test.ts
@@ -1549,6 +1549,9 @@ describe("Wikis Tools", () => {
     expect(() => schema.parse({ limit: 0 })).toThrow();
     expect(() => schema.parse({ limit: -5 })).toThrow();
     expect(() => schema.parse({ limit: 150 })).toThrow();
+    expect(() => schema.parse({ projectId: "" })).toThrow();
+    expect(() => schema.parse({ projectId: 0 })).toThrow();
+    expect(() => schema.parse({ projectId: -1 })).toThrow();
   });
 
   test("handleSearchWikiPages catches errors and returns error response", async () => {