diff --git a/server/app/views.py b/server/app/views.py
index e452a04..d47daad 100644
--- a/server/app/views.py
+++ b/server/app/views.py
@@ -10,12 +10,16 @@ from encryption import PrivateKey, PublicKey
 @route_post("users/new", args={'name': str, 'public_key': str})
 def create_user(params):
     "Creates a new user"
+    try:
+        PublicKey.load(params['public_key'])
+    except (ValueError, FileNotFoundError):
+        raise NotAllowed("Invalid public key")
     try:
         new_user = User.from_dict(params)
         new_user.save()
         return new_user.to_dict()
     except:
-        raise NotAllowed("Username and public key must be unique.")
+        raise NotAllowed(f"Username {params['name']} is already in use.")
 
 @route_get("users", args={'name': str})
 def get_user(params):