diff --git a/src/nameRecord.js b/src/nameRecord.js
index 932f387..c981557 100644
--- a/src/nameRecord.js
+++ b/src/nameRecord.js
@@ -28,10 +28,17 @@ export function validateName(name) {
   }
 
   if (name.startsWith("-")) {
-    throw new AppError(422, `Name '${name}' should not start with a hyphen.`);
+    throw new AppError(422, `Name '${name}' should not start with a hyphen -.`);
   }
 
   if (name.endsWith("-")) {
-    throw new AppError(422, `Name '${name}' should not start with a hyphen.`);
+    throw new AppError(422, `Name '${name}' should not start with a hyphen -.`);
+  }
+
+  if (name.includes("_")) {
+    throw new AppError(
+      422,
+      `Name '${name}' should not include an underscore _.`
+    );
   }
 }
diff --git a/test/app.test.js b/test/app.test.js
index 02ae124..ed6698b 100644
--- a/test/app.test.js
+++ b/test/app.test.js
@@ -144,6 +144,17 @@ describe("Nostr NIP 05 API tests", () => {
       .expect(422);
   });
 
+  it("should fail if the name includes an underscore", async () => {
+    const userData = createUserData({ name: "aa_" });
+
+    await request(app)
+      .post("/api/names")
+      .set("Host", "nos.social")
+      .set("Authorization", `Nostr ${nip98PostAuthToken}`)
+      .send(userData)
+      .expect(422);
+  });
+
   it("should fail if the name is not found", async () => {
     await request(app)
       .get("/.well-known/nostr.json")