diff --git a/app/models.py b/app/models.py
index 9043fb4..79473c4 100644
--- a/app/models.py
+++ b/app/models.py
@@ -1,6 +1,6 @@
 """Data models for the Workshop API."""
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 from typing import Optional
 
 
@@ -8,7 +8,7 @@ class ProfileCreate(BaseModel):
     """Schema for creating a new profile."""
 
     username: str
-    bio: str
+    bio: str = Field(..., max_length=500)
     age: Optional[int] = None
 
 
diff --git a/tests/test_profile.py b/tests/test_profile.py
index 6bf5e9f..7d0099d 100644
--- a/tests/test_profile.py
+++ b/tests/test_profile.py
@@ -29,3 +29,11 @@ def test_get_profile(clean_store):
 def test_get_nonexistent_profile(clean_store):
     response = client.get("/profile/nobody")
     assert response.status_code == 404
+
+
+def test_create_profile_with_too_long_bio(clean_store):
+    response = client.post(
+        "/profile",
+        json={"username": "alice", "bio": "x" * 501, "age": 22},
+    )
+    assert response.status_code == 422