diff --git a/locales/en-US.json b/locales/en-US.json
index 6c5625c3..2db67e0b 100644
--- a/locales/en-US.json
+++ b/locales/en-US.json
@@ -61,6 +61,7 @@
     "Sign Up": "Sign Up",
     "create_account_link_label": "Create an account",
     "sign_up_page_title": "Sign Up",
+    "registration_user_id_has_been_taken_error": "User ID has been taken",
     "E-mail": "E-mail",
     "Preferences": "Preferences",
     "preferences_category_player": "Player preferences",
diff --git a/src/invidious/routes/login.cr b/src/invidious/routes/login.cr
index d04eddca..78143121 100644
--- a/src/invidious/routes/login.cr
+++ b/src/invidious/routes/login.cr
@@ -101,6 +101,11 @@ module Invidious::Routes::Login
       return error_template(401, "User ID is a required field")
     end
 
+    # Ensure user doesn't exist
+    if Invidious::Database::Users.select(email: email)
+      return error_template(401, "registration_user_id_has_been_taken_error")
+    end
+
     if password.nil? || password.empty?
       return error_template(401, "Password cannot be empty")
     end